The compiler currently ICEs when compiling a stdarg function with
+nofp, as reported in PR 66258.

The aarch64.md file disables FP instructions using TARGET_FLOAT, which
supports both -mgeneral-regs-only and +nofp.  But there is code in
aarch64.c that checks TARGET_GENERAL_REGS_ONLY.  This results in FP
instructions when using +nofp,  The aarch64.c code needs to use
TARGET_FLOAT instead like the md file already does.

I can't meaningfully test this with a bootstrap, since the patch has
no effect unless I bootstrap with +nofp, and that will fail as gcc
contains floating point code.

The testsuite already has multiple stdarg tests, so there is no need
for another one.

I tested this by verifying I get the same results for some simple
testcasess with and without the patch, with and without using
-mgeneral-regs-only and -mcpu=cortex-a53+nofp.