fixincludes: Update darwin_flt_eval_method for macOS 14

fixincludes: Update darwin_flt_eval_method for macOS 14

On macOS 14, a guard in <math.h> changed:

-- MacOSX13.3.sdk/usr/include/math.h 2023-04-19 01:54:44
+++ MacOSX14.0.sdk/usr/include/math.h 2023-08-01 08:42:43
@@ -22,0 +23 @@
+
@@ -43 +44 @@
-#if __FLT_EVAL_METHOD__ == 0
+#if __FLT_EVAL_METHOD__ == 0 || __FLT_EVAL_METHOD__ == -1
@@ -49 +50 @@
-#elif __FLT_EVAL_METHOD__ == 2 || __FLT_EVAL_METHOD__ == -1
+#elif __FLT_EVAL_METHOD__ == 2

Therefore the darwin_flt_eval_method fixincludes fix doesn't match any
longer, leading to a large number of testsuite failures like

/private/var/gcc/regression/master/14-gcc/build/gcc/include-fixed/math.h:69:5:
error: #error "Unsupported value of __FLT_EVAL_METHOD__."

where __FLT_EVAL_METHOD__ = 16.

This patch adjusts the fix to allow for both forms.

Tested with make check in fixincludes on x86_64-apple-darwin23.0.0 and
verifying that <math.h> has indeed been fixed as expected.

(backport of 93f803d53b5ccaabded9d7b4512b54da81c1c616)

2023-12-11  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

fixincludes:
	* inclhack.def (darwin_flt_eval_method): Handle macOS 14 guard
	variant.
	* fixincl.x: Regenerate.
	* tests/base/math.h [DARWIN_FLT_EVAL_METHOD_CHECK]: Update test.