Pass use_default_shell_env = True for protoc (grpc#8984)

If protoc is compiled with MinGW it will depend on libstdc++-6.dll which is found in C:\msys64\mingw64\bin and can only be found by inheriting PATH from the environment.

java_grpc_library.bzl

@@ -93,6 +93,7 @@ def _java_rpc_library_impl(ctx):
         outputs = [srcjar],
         executable = toolchain.protoc,
         arguments = [args],
+        use_default_shell_env = True,
     )
 
     deps_java_info = java_common.merge([dep[JavaInfo] for dep in ctx.attr.deps])