Bug 1745344 - Unconditionally use va_copy. r=nika

Historically, va_copy was not supported everywhere (notably, MSVC didn't
have it). That's not true anymore. We already have code such as
xpcom/base/Logging.cpp that uses it unconditionally.

Differential Revision: https://phabricator.services.mozilla.com/D133458

mozglue/misc/Printf.cpp

@@ -30,18 +30,6 @@
 using double_conversion::DoubleToStringConverter;
 using DTSC = DoubleToStringConverter;
 
-/*
- * Note: on some platforms va_list is defined as an array,
- * and requires array notation.
- */
-#ifdef HAVE_VA_COPY
-#  define VARARGS_ASSIGN(foo, bar) VA_COPY(foo, bar)
-#elif defined(HAVE_VA_LIST_AS_ARRAY)
-#  define VARARGS_ASSIGN(foo, bar) foo[0] = bar[0]
-#else
-#  define VARARGS_ASSIGN(foo, bar) (foo) = (bar)
-#endif
-
 /*
  * Numbered Argument State
  */
@@ -654,7 +642,7 @@ static bool BuildArgArray(const char* fmt, va_list ap, NumArgStateVector& nas) {
     // earlier argument.
     MOZ_ASSERT(nas[cn].type != TYPE_UNKNOWN);
 
-    VARARGS_ASSIGN(nas[cn].ap, ap);
+    va_copy(nas[cn].ap, ap);
 
     switch (nas[cn].type) {
       case TYPE_SCHAR:

xpcom/base/nsCRTGlue.cpp

@@ -227,14 +227,6 @@ void NS_MakeRandomString(char* aBuf, int32_t aBufLen) {
 
 #endif
 
-#ifdef HAVE_VA_COPY
-#  define VARARGS_ASSIGN(foo, bar) VA_COPY(foo, bar)
-#elif defined(HAVE_VA_LIST_AS_ARRAY)
-#  define VARARGS_ASSIGN(foo, bar) foo[0] = bar[0]
-#else
-#  define VARARGS_ASSIGN(foo, bar) (foo) = (bar)
-#endif
-
 #if defined(XP_WIN)
 void vprintf_stderr(const char* aFmt, va_list aArgs) {
   if (IsDebuggerPresent()) {
@@ -244,7 +236,7 @@ void vprintf_stderr(const char* aFmt, va_list aArgs) {
       auto buf = MakeUnique<char[]>(lengthNeeded);
       if (buf) {
         va_list argsCpy;
-        VARARGS_ASSIGN(argsCpy, aArgs);
+        va_copy(argsCpy, aArgs);
         vsnprintf(buf.get(), lengthNeeded, aFmt, argsCpy);
         buf[lengthNeeded - 1] = '\0';
         va_end(argsCpy);