glibc: Pass linker choice via compiler flags

glibc configury tries to detect ld version and assumes BFD or gold
linker but when system ld is pointing to lld or mold it might fail the
linker check, therefore pass LD variable to explicitly point at ld.bfd
we are using BFD linker only to link glibc after all.

Second problem in such a case is that some partial objects are linked
with CC -r which will fail if we do not inform the compiler to use BFD
linker thusly pass it via appending to CC variable

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>