#70 Fix building with CLANG-9.0.0

[Peter Levine]

Building with CLANG-9.0.0 fails with:

clang-9: error: unknown argument: '-maccumulate-outgoing-args'

In Make.defaults, with GCCVERSION := $(shell $(CC) -dumpversion | cut -f1 -d.), GCCVERSION becomes 9. GCCNEWENOUGH then gets set to 1 and -maccumulate-outgoing-args is added to CPPFLAGS. Evaluating the USING_CLANG condition at the beginning of the if-then-else statement fixes it.

[Nigel Croxon]

commit 53b89f528ddf56dcf2ce58dff368ae4c960e4d40
Author: Callum Farmer gmbr3@opensuse.org
Date: Sat Jun 10 19:14:41 2023 +0100

X86_64: fix clang