inline.h: Use new C99 emulation

We don't have to know explicitly if the platform is 64 or 32 bits, and
can derive the constants that were formerly hard-coded in.

inline.h

@@ -387,24 +387,14 @@ S_is_utf8_invariant_string_loc(const U8* const s, STRLEN len, const U8 ** ep)
     send = s + len;
 
 #ifndef EBCDIC
-    /* Try to get the widest word on this platform */
-#  ifdef HAS_LONG_LONG
-#    define PERL_WORDCAST unsigned long long
-#    define PERL_WORDSIZE LONGLONGSIZE
-#  else
-#    define PERL_WORDCAST UV
-#    define PERL_WORDSIZE UVSIZE
-#  endif
-
-#  if PERL_WORDSIZE == 4
-#    define PERL_VARIANTS_WORD_MASK 0x80808080
-#    define PERL_WORD_BOUNDARY_MASK 0x3
-#  elif PERL_WORDSIZE == 8
-#    define PERL_VARIANTS_WORD_MASK UINT64_C(0x8080808080808080)
-#    define PERL_WORD_BOUNDARY_MASK 0x7
-#  else
-#    error Unexpected word size
-#  endif
+
+/* This looks like 0x010101... */
+#define PERL_COUNT_MULTIPLIER   (~ (UINTMAX_C(0)) / 0xFF)
+
+/* This looks like 0x808080... */
+#define PERL_VARIANTS_WORD_MASK (PERL_COUNT_MULTIPLIER * 0x80)
+#define PERL_WORDSIZE            sizeof(PERL_COUNT_MULTIPLIER)
+#define PERL_WORD_BOUNDARY_MASK (PERL_WORDSIZE - 1)
 
     /* Process per-byte until reach word boundary.  XXX This loop could be
      * eliminated if we knew that this platform had fast unaligned reads */
@@ -421,7 +411,7 @@ S_is_utf8_invariant_string_loc(const U8* const s, STRLEN len, const U8 ** ep)
 
     /* Process per-word as long as we have at least a full word left */
     while (x + PERL_WORDSIZE <= send) {
-        if ((* (PERL_WORDCAST *) x) & PERL_VARIANTS_WORD_MASK)  {
+        if ((* (uintmax_t *) x) & PERL_VARIANTS_WORD_MASK)  {
 
             /* Found a variant.  Just return if caller doesn't want its exact
              * position */