Restore ld_bfd finding libgcc to link with it, fix bootstrap build for linux-armhf

[illwieckz]

Restore ld_bfd finding libgcc to link with it, fix bootstrap build for linux-armhf.

Fixup for:

• Allow building with Clang without installing GCC #26

Fixes:

arm-linux-gnueabihf-ld.bfd: nacl_bootstrap.dir/nacl_bootstrap.c.o: in function `iov_int_string':
nacl_bootstrap.c:118: undefined reference to `__aeabi_idivmod'

[slipher]

How are you using it? It works for me in the Scons build for both GCC and Clang. With Clang (scons --mode=opt-host,nacl saigo=1 werror=0 platform=arm all_programs -j9) the command issued is:

env CXX='/usr/bin/clang++' /usr/bin/python3 /unv/nacl/src/trusted/service_runtime/linux/ld_bfd.py --compiler arm-linux-gnueabihf-g++ -m armelf_linux_eabi --build-id -static -z max-page-size=0x1000 --orphan-handling=discard --defsym RESERVE_TOP=0x40002000 --script /unv/nacl/src/trusted/service_runtime/linux/nacl_bootstrap.x -o scons-out/opt-linux-arm/obj/src/trusted/service_runtime/nacl_bootstrap_raw scons-out/opt-linux-arm/obj/src/trusted/service_runtime/linux/nacl_bootstrap.o

With GCC (scons --mode=opt-host,nacl saigo=1 werror=0 platform=arm all_programs -j9 --no-clang) the command issued is:

env CXX='arm-linux-gnueabihf-g++' /usr/bin/python3 /unv/nacl/src/trusted/service_runtime/linux/ld_bfd.py --compiler arm-linux-gnueabihf-g++ -m armelf_linux_eabi --build-id -static -z max-page-size=0x1000 --orphan-handling=discard --defsym RESERVE_TOP=0x40002000 --script /unv/nacl/src/trusted/service_runtime/linux/nacl_bootstrap.x -o scons-out/opt-linux-arm/obj/src/trusted/service_runtime/nacl_bootstrap_raw scons-out/opt-linux-arm/obj/src/trusted/service_runtime/linux/nacl_bootstrap.o

Anyway surely you don't need this junk? It was described as only being needed to avoid using gold but that hardly exists any more. I would have gotten rid of it but didn't feel like untangling everything at the moment. For a new build surely you could just set it in the toolchain file or whatever.

[slipher]

Shouldn't adding libgcc be inside the g++ detection block?

[slipher]

Never mind, I remember now that the "g++" string depends on what architecture was used, not what compiler...

[illwieckz]

You can have a libgcc on the system you compile with clang for, what matters there is to find libgcc when it's present (and then, less likely to be used).

[slipher]

This is OK to merge as it doesn't break anything. Though I wonder if there is some unintended difference in the build that makes this required. And with the caveat that it would be probably nicer to just call the desired linker directly.