[HTML5] Raise default initial memory to 32 MiB.

The memory was resized in any case during start.

Mitigate Chromium issue:
https://bugs.chromium.org/p/v8/issues/detail?id=11863

Also fix a warning about SAFE_HEAP being a linker only flag.

(cherry picked from commit 897c906ebfd1736b27dd8aadd19c18da8a38dee2)

platform/javascript/detect.py

@@ -29,7 +29,7 @@ def get_opts():
     from SCons.Variables import BoolVariable
 
     return [
-        ("initial_memory", "Initial WASM memory (in MiB)", 16),
+        ("initial_memory", "Initial WASM memory (in MiB)", 32),
         BoolVariable("use_assertions", "Use Emscripten runtime assertions", False),
         BoolVariable("use_thinlto", "Use ThinLTO", False),
         BoolVariable("use_ubsan", "Use Emscripten undefined behavior sanitizer (UBSAN)", False),
@@ -126,7 +126,6 @@ def configure(env):
         env.Append(CCFLAGS=["-fsanitize=leak"])
         env.Append(LINKFLAGS=["-fsanitize=leak"])
     if env["use_safe_heap"]:
-        env.Append(CCFLAGS=["-s", "SAFE_HEAP=1"])
         env.Append(LINKFLAGS=["-s", "SAFE_HEAP=1"])
 
     # Closure compiler