gen_compile_commands: Ignore libgcc.a

gen_compile_commands: Ignore libgcc.a

Some architectures link libgcc.a from the toolchain into the kernel.
gen_compile_commands trie to read the kbuild .cmd files of its
constituent object files, which are not available.

Flat out ignore libgcc.a, as it is not built as part of the kernel
anyways.

Link: https://lore.kernel.org/r/20260427-kunit-or1k-v1-1-9d3109e991e8@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>