gcc: synchronize with toolchain

gcc: synchronize with toolchain

Modify the gcc package to support building 13.4.0, 14.3.0, and 15.2.0,
which are the same versions supported by the current toolchain.

Upstream list of changes can be found at:

	https://gcc.gnu.org/gcc-13/changes.html
	https://gcc.gnu.org/gcc-14/changes.html
	https://gcc.gnu.org/gcc-15/changes.html

Signed-off-by: W. Michael Petullo <redacted>