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>

module/os/linux/spl/spl-generic.c

@@ -225,8 +225,10 @@ __div_u64(uint64_t u, uint32_t v)
  * replacements for libgcc-provided functions and will never be called
  * directly.
  */
+#if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wmissing-prototypes"
+#endif
 
 /*
  * Implementation of 64-bit unsigned division for 32-bit machines.
@@ -425,7 +427,9 @@ __aeabi_ldivmod(int64_t u, int64_t v)
 EXPORT_SYMBOL(__aeabi_ldivmod);
 #endif /* __arm || __arm__ */
 
+#if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic pop
+#endif
 
 #endif /* BITS_PER_LONG */