Bug 1570499 - Part 2: Suppress -Wimplicit-fallthrough warnings from third-party udis86 code. r=froydnj

ProcessRedirect.cpp includes third-party udis86 C code that triggers -Wimplicit-fallthrough warnings. We suppress these warnings in ProcessRedirect.cpp because we want to minimize Mozilla changes to third-party code and we can't use C++17's [[fallthrough]] attribute in C code anyway. We don't suppress the warnings for the entire ProcessRedirect.cpp file (e.g. in moz.build) because we'd like clang -Wimplicit-fallthrough to check ProcessRedirect.cpp's own use of [[fallthrough]].

This changeset reverts some earlier Mozilla changes [1] made to upstream udis86's decode.c [2] that are no longer necessary.

[1] https://hg.mozilla.org/mozilla-central/rev/9042673fb235c00fbb021ea6356f4b0921505d1d
[2] https://github.com/vmt/udis86/blob/master/libudis86/decode.c#L747

Differential Revision: https://phabricator.services.mozilla.com/D56441

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

toolkit/recordreplay/ProcessRedirect.cpp

@@ -15,6 +15,11 @@
 #include <dlfcn.h>
 #include <string.h>
 
+#if defined(__clang__)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wimplicit-fallthrough"
+#endif
+
 namespace {
 
 #include "udis86/udis86.c"
@@ -23,6 +28,10 @@ namespace {
 
 }  // anonymous namespace
 
+#if defined(__clang__)
+#  pragma clang diagnostic pop
+#endif
+
 namespace mozilla {
 namespace recordreplay {
 

toolkit/recordreplay/udis86/decode.c

@@ -648,12 +648,12 @@ decode_operand(struct ud           *u,
       break;
     case OP_F:
       u->br_far  = 1;
-      MOZ_FALLTHROUGH;
+      /* intended fall through */
     case OP_M:
       if (MODRM_MOD(modrm(u)) == 3) {
         UDERR(u, "expected modrm.mod != 3\n");
       }
-      MOZ_FALLTHROUGH;
+      /* intended fall through */
     case OP_E:
       decode_modrm_rm(u, operand, REGCLASS_GPR, size);
       break;
@@ -672,7 +672,7 @@ decode_operand(struct ud           *u,
       if (MODRM_MOD(modrm(u)) != 3) {
         UDERR(u, "expected modrm.mod == 3\n");
       }
-      MOZ_FALLTHROUGH;
+      /* intended fall through */
     case OP_Q:
       decode_modrm_rm(u, operand, REGCLASS_MMX, size);
       break;
@@ -683,7 +683,7 @@ decode_operand(struct ud           *u,
       if (MODRM_MOD(modrm(u)) != 3) {
         UDERR(u, "expected modrm.mod == 3\n");
       }
-      MOZ_FALLTHROUGH;
+      /* intended fall through */
     case OP_W:
       decode_modrm_rm(u, operand, REGCLASS_XMM, size);
       break;