Fix x86 ClangCL and GCC/Clang -std=c## compiles

[p0lymeric]

Checklist

• if this fixes something: added a Fixes: tag to the commit message

Fixes compile for some x86 compiler configurations, including ClangCL on Windows, and GCC/Clang in Standard C mode (-std=c##).

Fixes #767

Notes:

• Reintroduced some nasty-looking parts from this past commit (aes_desc.c:L66-78):
  • ec3804c#diff-4b49c40dd5787d702d14e1859464a5941919a8dd8288dce824014f07939e321eL66-L78
• ClangCL is handled by falling through defined(_MSC_VER) && !defined(__clang__) into the GNU-style inline asm block
• __asm__ instead of asm so that gcc/clang accept the inline asm block in Standard C mode

[karel-m]

there already exists a similar patch e9a7e94 in #755

[p0lymeric]

I agree, e9a7e94 covers the -std=c## case. Thank you, did not see that patch.

This PR also has a fix for ClangCL compilation. A previous cleanup commit (ec3804c) removed the && !defined(__clang__) factor from the #if defined(_MSC_VER) check, in the function that became s_x86_cpuid.

[karel-m]

@p0lymeric FYI the __asm__ part is now fixed in develop

I am not sure about the ugly hack #if defined(_MSC_VER) && !defined(__clang__) ...

Isn't it about missing #include <intrin.h> ?

I am not using ClangCL but if it tries to pretend to be GNUC and MSVC at once then this might be a problem:

#if defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
#pragma GCC diagnostic ignored "-Wdeclaration-after-statement"
#pragma GCC diagnostic ignored "-Wuninitialized"
#pragma GCC diagnostic ignored "-Wunused-function"
#elif defined(_MSC_VER)
#include <intrin.h>
#endif