build: do not hardcode the compiler when building llvm using autotools
build: do not hardcode the compiler when building llvm using autotools

Not every system has gcc-5 and if it does, it may be named just gcc.
check available compilers and pick the right one.

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>

staticafi/symbiotic,staticafi/symbiotic,staticafi/symbiotic,staticafi/symbiotic