[CMake] cross g++ linking shared instead of static libgcc

[Darren Hollenbeck]

I am using CMake to cross compile with an arm toolchain and getting a linker
error:
undefined reference to `__sync_fetch_and_add_4'

the toolchain has both a shared and static libgcc:
./lib/gcc/arm-linux-gnueabi/4.5.2/libgcc.a
./lib/gcc/arm-linux-gnueabi/4.5.2/libgcc_eh.a
./arm-linux-gnueabi/lib/libgcc_s.so.1
./arm-linux-gnueabi/lib/libgcc_s.so

the path for both is in the linker directories (from CMakeCXXCompiler.cmake
generated in the build directory/CMakeFiles), but the path for the static is
first:
SET(CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES
"/opt/gatecraft/arm/lib/gcc/arm-linux-gnueabi/4.5.2;/opt/gatecraft/arm/arm-linux-gnueabi/lib;/opt/gatecraft/arm/arm-linux-gnueabi/usr/lib")

The libraries are not the same, the .so does not have the symbol the linker
is complaining about but the .a does (I inspected this with nm). What I
can't figure out is why I can switch the CMAKE_CXX_COMPILER defined in my
toolchain file to another toolchain (with the same shared/static and linker
path order) - keeping everything else the same - and the build succeeds. I
can't find any significant difference in anything in the build directory
between the two, yet one will link libgcc.a (and therefore works) and the
other won't (and gives the error above).

I found that I have a work-around by forcing -static-libgcc in the linker
flags, but this doesn't explain why it works without this change when I
switch the compiler to the other toolchain.


Anyone able to explain the discrepancy here and offer a fix?
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