Add some missing stdarg includes

One of our internal Chromecast builds was failing due to undefined
va_list in wasm-result.h. I also searched for other files where va_list
was used without including stdarg.h and added it as necessary (since
include-what-you-use is a thing).

BUG=chromium:706443

Review-Url: https://codereview.chromium.org/2780913002
Cr-Commit-Position: refs/heads/master@{#44588}

src/base/logging.cc

@@ -4,6 +4,7 @@
 
 #include "src/base/logging.h"
 
+#include <cstdarg>
 #include <cstdio>
 #include <cstdlib>
 

src/heap/gc-tracer.cc

@@ -4,6 +4,8 @@
 
 #include "src/heap/gc-tracer.h"
 
+#include <cstdarg>
+
 #include "src/counters.h"
 #include "src/heap/heap-inl.h"
 #include "src/isolate.h"

src/wasm/decoder.h

@@ -5,6 +5,7 @@
 #ifndef V8_WASM_DECODER_H_
 #define V8_WASM_DECODER_H_
 
+#include <cstdarg>
 #include <memory>
 
 #include "src/base/compiler-specific.h"

src/wasm/wasm-result.h

@@ -5,6 +5,7 @@
 #ifndef V8_WASM_RESULT_H_
 #define V8_WASM_RESULT_H_
 
+#include <cstdarg>
 #include <memory>
 
 #include "src/base/compiler-specific.h"