linpengt@linpengt-mbp:~/workspace/cppformat$ g++ --version
g++ (Homebrew gcc 4.9.1) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

linpengt@linpengt-mbp:~/workspace/cppformat$ CXX=g++ CC=gcc cmake .
-- CMake version: 3.0.2
-- The C compiler identification is GNU 4.9.1
-- The CXX compiler identification is GNU 4.9.1
-- Checking whether C compiler has -isysroot
-- Checking whether C compiler has -isysroot - yes
-- Checking whether C compiler supports OSX deployment target flag
-- Checking whether C compiler supports OSX deployment target flag - yes
-- Check for working C compiler: /usr/bin/gcc
-- Check for working C compiler: /usr/bin/gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Check for working CXX compiler: /usr/bin/g++
-- Check for working CXX compiler: /usr/bin/g++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Build type: Release
-- Performing Test HAVE_STD_CPP11_FLAG
-- Performing Test HAVE_STD_CPP11_FLAG - Success
-- Looking for open
-- Looking for open - found
-- Target 'doc' disabled (requires doxygen)
-- Looking for include file pthread.h
-- Looking for include file pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - found
-- Found Threads: TRUE
-- Performing Test FMT_VARIADIC_TEMPLATES
-- Performing Test FMT_VARIADIC_TEMPLATES - Success
-- Performing Test HAVE_TYPE_TRAITS
-- Performing Test HAVE_TYPE_TRAITS - Success
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG - Success
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/linpengt/workspace/cppformat
linpengt@linpengt-mbp:~/workspace/cppformat$ make
Scanning dependencies of target format
[  3%] Building CXX object CMakeFiles/format.dir/format.cc.o
[  7%] Building CXX object CMakeFiles/format.dir/posix.cc.o
Linking CXX static library libformat.a
[  7%] Built target format
Scanning dependencies of target gmock
[ 11%] Building CXX object CMakeFiles/gmock.dir/gmock/gmock-gtest-all.cc.o
Linking CXX static library libgmock.a
[ 11%] Built target gmock
Scanning dependencies of target test-main
[ 14%] Building CXX object test/CMakeFiles/test-main.dir/test-main.cc.o
[ 18%] Building CXX object test/CMakeFiles/test-main.dir/gtest-extra.cc.o
[ 22%] Building CXX object test/CMakeFiles/test-main.dir/util.cc.o
Linking CXX static library libtest-main.a
[ 22%] Built target test-main
Scanning dependencies of target format-impl-test
[ 25%] Building CXX object test/CMakeFiles/format-impl-test.dir/format-impl-test.cc.o
Linking CXX executable format-impl-test
[ 25%] Built target format-impl-test
Scanning dependencies of target format-test
[ 29%] Building CXX object test/CMakeFiles/format-test.dir/format-test.cc.o
Linking CXX executable format-test
[ 29%] Built target format-test
Scanning dependencies of target gtest-extra-test
[ 33%] Building CXX object test/CMakeFiles/gtest-extra-test.dir/gtest-extra-test.cc.o
Linking CXX executable gtest-extra-test
[ 33%] Built target gtest-extra-test
Scanning dependencies of target header-only-test
[ 37%] Building CXX object test/CMakeFiles/header-only-test.dir/header-only-test.cc.o
[ 40%] Building CXX object test/CMakeFiles/header-only-test.dir/header-only-test2.cc.o
[ 44%] Building CXX object test/CMakeFiles/header-only-test.dir/test-main.cc.o
Linking CXX executable header-only-test
duplicate symbol int fmt::internal::CharTraits<char>::format_float<double>(char*, unsigned long, char const*, unsigned int, int, double) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol int fmt::internal::CharTraits<char>::format_float<long double>(char*, unsigned long, char const*, unsigned int, int, long double) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol int fmt::internal::CharTraits<wchar_t>::format_float<double>(wchar_t*, unsigned long, wchar_t const*, unsigned int, int, double) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol int fmt::internal::CharTraits<wchar_t>::format_float<long double>(wchar_t*, unsigned long, wchar_t const*, unsigned int, int, long double) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::BasicFormatter<char>::format(char const*&, fmt::internal::Arg const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::BasicFormatter<char>::format(fmt::BasicStringRef<char>, fmt::ArgList const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::internal::PrintfFormatter<char>::format(fmt::BasicWriter<char>&, fmt::BasicStringRef<char>, fmt::ArgList const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::BasicFormatter<wchar_t>::format(wchar_t const*&, fmt::internal::Arg const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::BasicFormatter<wchar_t>::format(fmt::BasicStringRef<wchar_t>, fmt::ArgList const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
duplicate symbol fmt::internal::PrintfFormatter<wchar_t>::format(fmt::BasicWriter<wchar_t>&, fmt::BasicStringRef<wchar_t>, fmt::ArgList const&) in:
    CMakeFiles/header-only-test.dir/header-only-test.cc.o
    CMakeFiles/header-only-test.dir/header-only-test2.cc.o
ld: 10 duplicate symbols for architecture x86_64
collect2: error: ld returned 1 exit status
make[2]: *** [test/header-only-test] Error 1
make[1]: *** [test/CMakeFiles/header-only-test.dir/all] Error 2
make: *** [all] Error 2