Fix win32 build.

Follow up to aosp/1711913.
Fix a copy/paste mistake in platform_windows.cc
(PerfettoOnThreadExit vs OnThreadExit) which caused
a failure in the win32-archive-dbg/rel chromium
bots (https://ci.chromium.org/b/8846610513401740704).
This CL also makes it possible to build for win32
setting target_cpu=host_cpu="x86" in our standalone
build.
Also temporarily exclude some tests that fail on MSVC.

Bug: 174454879
Change-Id: I038b252020c68a4f3344441f3797f4786d94dd0b
diff --git a/gn/standalone/BUILD.gn b/gn/standalone/BUILD.gn
index 31941ed..ffe5725 100644
--- a/gn/standalone/BUILD.gn
+++ b/gn/standalone/BUILD.gn
@@ -209,10 +209,10 @@
     ldflags += [ "-flto=full" ]
   }
 
-  # We support only x64 builds on Windows.
-  assert(!is_win || current_cpu == "x64")
-
-  if (current_cpu == "arm") {
+  if (is_win) {
+    # We support only x86/x64 builds on Windows.
+    assert(current_cpu == "x64" || current_cpu == "x86")
+  } else if (current_cpu == "arm") {
     cflags += [
       "-march=armv7-a",
       "-mfpu=neon",