Bug 1661810 - Define pre_align/post_align based on the compiler. r=jcj

Things worked fine before we upgraded to clang 11 presumably because the
stack was always 16-bytes aligned in the first place, or something akin
to that, and the lack of pre_align/post_align doing anything didn't
matter. The runtime misalignment of the stack may well be a clang > 9
bug, but keeping pre_align/post_align tied to the x86/x64 is a footgun
anyways.

Differential Revision: https://phabricator.services.mozilla.com/D88667

--HG--
extra : moz-landing-system : lando

lib/freebl/blapii.h

@@ -60,10 +60,10 @@ SEC_END_PROTOS
 #endif
 
 /* Alignment helpers. */
-#if defined(_WINDOWS) && defined(NSS_X86_OR_X64)
+#if defined(_MSC_VER)
 #define pre_align __declspec(align(16))
 #define post_align
-#elif defined(NSS_X86_OR_X64)
+#elif defined(__GNUC__)
 #define pre_align
 #define post_align __attribute__((aligned(16)))
 #else