Replace FALLTHROUGH macro with C++17 [[fallthrough]] attribute

See go/chromium-lsc-fallthrough

Bug:1283907
Change-Id: I786f3e7141ad47913043136d0173e3b82b223a87
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/3370128
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>
diff --git a/handler/linux/exception_handler_server.cc b/handler/linux/exception_handler_server.cc
index c9fbb0a..aef252f 100644
--- a/handler/linux/exception_handler_server.cc
+++ b/handler/linux/exception_handler_server.cc
@@ -198,7 +198,7 @@
         if (HaveCapSysPtrace()) {
           return Strategy::kDirectPtrace;
         }
-        FALLTHROUGH;
+        [[fallthrough]];
       case PtraceScope::kNoAttach:
         LOG(WARNING) << "no ptrace";
         return Strategy::kNoPtrace;
diff --git a/snapshot/minidump/process_snapshot_minidump.cc b/snapshot/minidump/process_snapshot_minidump.cc
index db7e595..8c870ee 100644
--- a/snapshot/minidump/process_snapshot_minidump.cc
+++ b/snapshot/minidump/process_snapshot_minidump.cc
@@ -323,7 +323,7 @@
       full_version_ = base::UTF16ToUTF8(info.BuildString);
 #endif
       full_version_ = full_version_.substr(0, full_version_.find(';'));
-      FALLTHROUGH;
+      [[fallthrough]];
     case sizeof(MINIDUMP_MISC_INFO_3):
     case sizeof(MINIDUMP_MISC_INFO_2):
     case sizeof(MINIDUMP_MISC_INFO):