Fix Clang 15 compilation errors

• Clang 15 doesn't support -fno-ipa-sra anymore. Do a separate check for -fno-ipa-sra support by $KERNEL_CC.

• Don't enable -mgeneral-regs-only for certain module files. Fix #13260

• Scope GCC diagnostic ignored statements to GCC only. Clang doesn't need them to compile the code.

Porting notes:

• Moved the stanzas removing -mgeneral-regs-only to Makefile.in since they wouldn't readily work in Kbuild.in and that did.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #13260
Closes #14150

Closes #14624
Ported-by: Rich Ercolani <rincebrain@gmail.com
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>