Revert "Build with C11 on MSVC in the standalone Bazel build"

This reverts commit 28e4a1b. Bazel
broke --cxxopt on Windows in
bazelbuild/bazel#15073, which means projects
enabling, say, C++20 with --cxxopt=/std:c++20 are silently passing
/std:c++20 to our C files.

This is already a problem, but MSVC is smart enough to silently ignore
the flag when building C. However, MSVC will report an error if you then
pass /std:c++20 /std:c11 into the same command. It seems that check is
not aware of this ignoring behavior.

Ultimately, this is a Bazel bug, and one that makes the broken versions
of Bazel unsuitable for use with C. This was fixed in Bazel in
bazelbuild/bazel#18119 and backported to the
upcoming Bazel 6.3.0 release in
bazelbuild/bazel#18552

Temporarily revert the change. When Bazel 6.3.0 is released, we'll put
this back and require Windows users use a functioning version of Bazel.

Bug: 624
Fixed: 623
Change-Id: I68d9b2ed8751b4cf5dc7f42f8c1fbd42a97d6ca2
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/61365
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>

util/BUILD.toplevel

@@ -121,7 +121,10 @@ boringssl_copts = [
 }) + asm_copts
 
 boringssl_copts_c11 = boringssl_copts + select({
-    "@platforms//os:windows": ["/std:c11"],
+    # TODO(crbug.com/boringssl/624): This should pass /std:c11 on MSVC. It was
+    # reverted due to https://github.com/bazelbuild/bazel/issues/15073. When
+    # Bazel 6.3.0 is released, restore it and require C11 on MSVC.
+    "@platforms//os:windows": [],
     "//conditions:default": gcc_copts_c11,
 })