Need to place static proc objects into 8-byte alignments

Static proc objects defined as methods may be placed in 4-byte alignments in 32-bit environments.
This may be misinterpreted as an immediate value depending on the address.

Since C11 and C++11 have additional language features for byte alignment, corresponding compilers use them to define the `mrb_alignas()` macro.
For earlier compilers, they use their own extensions to define the `mrb_alignas()` macro.

GCC supports `__attribute__((aligned(alignment)))` since at least version 2.95.3 (1999).
https://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_4.html#IDX305
According to GPT-4, support was added in version 2.7 (1995).

It is not known which version of Visual C++ added support for `__declspec(align(n))`.
According to GPT-4, at least Visual C++ 6.0 (1998) seems to support it.
Also, the documentation of past Intel C/C++ compilers that support `__declspec(align(n))` makes reference to support with Visual C++ 4.2 (1996).
https://www.intel.com/content/dam/www/public/ijkk/jp/ja/documents/developer/ccomp40j.pdf

include/mruby/common.h

@@ -59,6 +59,26 @@ MRB_BEGIN_DECL
 # define mrb_deprecated
 #endif
 
+/** Declare a type or object as an alignment requirement. */
+#ifndef mrb_alignas
+# if defined(__cplusplus) && __cplusplus >= 201103L
+#  // https://en.cppreference.com/w/cpp/language/alignas
+#  define mrb_alignas(n) alignas(n)
+# elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
+#  // https://en.cppreference.com/w/c/language/_Alignas
+#  define mrb_alignas(n) _Alignas(n)
+# elif defined(_MSC_VER) || defined(__INTEL_COMPILER)
+#  // https://learn.microsoft.com/en-us/cpp/cpp/align-cpp?view=msvc-170
+#  define mrb_alignas(n) __declspec(align(n))
+# elif defined(__GNUC__) || defined(__clang__)
+#  // https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-aligned-type-attribute
+#  define mrb_alignas(n) __attribute__((aligned(n)))
+# else
+#  // `mrb_alignas` defined as dummy. If necessary, send issues to https://github.com/mruby/mruby .
+#  define mrb_alignas(n)
+# endif
+#endif
+
 /** Declare a function as always inlined. */
 #if defined _MSC_VER && _MSC_VER < 1900
 # ifndef __cplusplus

mrbgems/mruby-catch/src/catch.c

@@ -37,6 +37,7 @@ static const mrb_irep catch_irep = {
   NULL,
   sizeof(catch_iseq),0,3,0,0
 };
+mrb_alignas(8)
 static const struct RProc catch_proc = {
   NULL, NULL, MRB_TT_PROC, MRB_GC_RED, MRB_FL_OBJ_IS_FROZEN | MRB_PROC_SCOPE | MRB_PROC_STRICT,
   { &catch_irep }, NULL, { NULL }

src/class.c

@@ -2915,6 +2915,7 @@ static const mrb_irep new_irep = {
   sizeof(new_iseq), 0, 2, 0, 0,
 };
 
+mrb_alignas(8)
 static const struct RProc new_proc = {
   NULL, NULL, MRB_TT_PROC, MRB_GC_RED, MRB_FL_OBJ_IS_FROZEN | MRB_PROC_SCOPE | MRB_PROC_STRICT,
   { &new_irep }, NULL, { NULL }

src/proc.c

@@ -36,6 +36,7 @@ static const mrb_irep call_irep = {
   0,                                   /* refcnt */
 };
 
+mrb_alignas(8)
 static const struct RProc call_proc = {
   NULL, NULL, MRB_TT_PROC, MRB_GC_RED, MRB_FL_OBJ_IS_FROZEN | MRB_PROC_SCOPE | MRB_PROC_STRICT,
   { &call_irep }, NULL, { NULL }