Fix LTO with GCC 4.9

[Tilka]

For LTO to work, GCC 4.9 requires using the wrappers gcc-ar and gcc-ranlibs:
http://gcc.gnu.org/gcc-4.9/changes.html

CMake doesn't account for this yet:
http://public.kitware.com/pipermail/cmake-developers/2014-January/009344.html

[magumagu]

Do we need to check the gcc version?

[Tilka]

No, unless you want to support GCC versions older than 4.7. I usually take Debian stable as a baseline (see Debian buildslave).

[magumagu]

Okay; just wanted to make sure you considered it.

[Sonicadvance1]

Causes build to fail with GCC 4.8.1

[Tilka]

As discussed on IRC:

Ubuntu saucy's gcc package doesn't add a gcc-ar --> gcc-ar-4.x symlink. My response would be to just accept the fact that LTO is (currently) broken on saucy (it's fixed in trusty).

[Sonicadvance1]

If it's Ubuntu failing then I have no reason to not say LGTM.

[Tilka]

@sheepdestroyer: Does it compile without ccache or with an empty cache? Either way, can you compile with make -j1 V=1 so we can see the command line that fails? Please paste that somewhere to keep this PR readable (I shortened your comment a bit).

[sheepdestroyer]

[sheepdestroyer@sheepora Build]$ ccache -C
Cleared cache
[sheepdestroyer@sheepora Build]$ make -j 1 V=1
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/dis_decode.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/dis_groups.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/resolve.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/syntax.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/PowerPCDisasm.cpp.o
Linking CXX static library libbdisasm.a
/usr/bin/ar terminated with signal 11 [Segmentation fault], core dumped
make[2]: *** [Externals/Bochs_disasm/libbdisasm.a] Error 1
make[1]: *** [Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/all] Error 2
make: *** [all] Error 2
[sheepdestroyer@sheepora Build]$ 

[Tilka]

What happens when you don't use ccache but use GCC directly?

[sheepdestroyer]

[sheepdestroyer@sheepora Build]$ export CCACHE_DISABLE=1
[sheepdestroyer@sheepora Build]$ ccache -C
Cleared cache
[sheepdestroyer@sheepora Build]$ make clean
[sheepdestroyer@sheepora Build]$ CCACHE_DISABLE=1 make -j 1 V=1
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/dis_decode.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/dis_groups.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/resolve.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/syntax.cpp.o
[  0%] Building CXX object Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/PowerPCDisasm.cpp.o
Linking CXX static library libbdisasm.a
/usr/bin/ar terminated with signal 11 [Segmentation fault], core dumped
make[2]: *** [Externals/Bochs_disasm/libbdisasm.a] Error 1
make[1]: *** [Externals/Bochs_disasm/CMakeFiles/bdisasm.dir/all] Error 2
make: *** [all] Error 2

is there a better way to do it?

[Tilka]

Sorry, it's make -j1 VERBOSE=1. Can you try again?

[sheepdestroyer]

http://pastebin.com/xhnEyt1A

[Tilka]

@sheepdestroyer: No idea, have you tried it completely without ccache? Just use a different build directory.

Native CMake support is kinda stalled: http://public.kitware.com/pipermail/cmake-developers/2014-January/009344.html

[sheepdestroyer]

ran it again from a new folder with CCACHE_DISABLE=1 make -j1 VERBOSE=1 but with same result :
http://pastebin.com/2mNFqNeK

[Tilka]

@sheepdestroyer You're still calling ccache, you probably need to unset CC; unset CXX.

[sheepdestroyer]

It was not ccache but a bug with binutils, this post from someone with a similar error put me on it :
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53831

My system originally had binutils 2.24.14 and after building binutils 2.24.51 from git I can now successfully build and run dolphin with gcc 4.9 and lto