Bug 1974917 - Fix TypeToString to automatically handle named/numbered int types. r=nbp,glandium a=RyanVM

`TypeToString` defines instances for all the numbered int types (like
`int32_t`); unfortunately this can leave some of the named types (like
`int`) out of the sequence depending on how the C headers define the
numbered ones.  There are additional instances for signed and unsigned
long, which are needed on some platforms and would break the build on
others; there is an `#ifdef` which attempts to handle that, but the
result of all this is that CI can build for 32-bit x86 Linux but it
fails when I try locally.

This patch simplifies things and removes the `#ifdef` using a similar
idea to bug 836438: the unspecialized `TypeToString` calls another
function with its own set of specializations, with numbered types in the
first layer and named types in the second.

mfbt/Casting.h

@@ -83,7 +83,12 @@ constexpr uint64_t safe_integer_unsigned() {
 }
 
 template <typename T>
-const char* TypeToString();
+const char* TypeToStringFallback();
+
+template <typename T>
+inline constexpr const char* TypeToString() {
+  return TypeToStringFallback<T>();
+}
 
 #define T2S(type)                                     \
   template <>                                         \
@@ -91,6 +96,12 @@ const char* TypeToString();
     return #type;                                     \
   }
 
+#define T2SF(type)                                            \
+  template <>                                                 \
+  inline constexpr const char* TypeToStringFallback<type>() { \
+    return #type;                                             \
+  }
+
 T2S(uint8_t);
 T2S(uint16_t);
 T2S(uint32_t);
@@ -101,14 +112,15 @@ T2S(int32_t);
 T2S(int64_t);
 T2S(char16_t);
 T2S(char32_t);
-#if defined(XP_DARWIN) || defined(XP_WIN) || defined(__wasm__)
+T2SF(int);
-T2S(long);
+T2SF(unsigned int);
-T2S(unsigned long);
+T2SF(long);
-#endif
+T2SF(unsigned long);
 T2S(float);
 T2S(double);
 
 #undef T2S
+#undef T2SF
 
 template <typename In, typename Out>
 inline void DiagnosticMessage(In aIn, char aDiagnostic[1024]) {