feat(build): allow additional CFLAGS for library build

Current CFLAGS if set for library builds could impact entire build, so
allow to pass additional CFLAGs for library builds based on format
<LIBNAME>_CFLAGS.

This support is currently needed to avoid 'redundant declaration'
error from latest mbedtls-3.3, the issue is reported to mbedtls[1]
and is under consideration to remove any redundant declarations.
But till then we have to disable that compiler option while building
for mbedtls-3.3

[1]: https://github.com/Mbed-TLS/mbedtls/issues/6910



Change-Id: Ic99af22b229f8089c82110d6545f762c14a62f5c
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>