PR gdb/30214: Prefer local include paths to system include paths

Some systems may install binutils headers into a system location
(e.g. /usr/local/include on FreeBSD) which may also include headers
for other external packages used by GDB such as zlib or zstd.  If a
system include path such as /usr/local/include is added before local
include paths to directories within a clone or release tarball, then
headers from the external binutils package are used which can result
in build failures if the external binutils package is out of sync with
the version of GDB being built.

To fix, sort the include paths in INTERNAL_CFLAGS_BASE to add CFLAGS
for "local" componenets before external components.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30214


Reviewed-By: Tom Tromey <tom@tromey.com>