Fix GCC errors

Summary:
These build failures only happen with GCC opt which I didn't test before submitting the GCC 10 upgrade.

UPB inside of GRPC has an issues with GCC-10 and this disables the relevant warnings.

Test Plan: N/A

Reviewers: oazizi, philkuz, #engineering

Reviewed By: oazizi, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D5709

GitOrigin-RevId: eb6524f5985ae5d6cea1601df73107a6b02908de

.bazelrc

@@ -60,7 +60,12 @@ build:gcc --action_env=BAZEL_CXXOPTS=-std=c++17
 build:gcc --action_env=BAZEL_COMPILER=gcc
 build:gcc --action_env=CC=/usr/bin/gcc-10
 build:gcc --action_env=CXX=/usr/bin/g++-10
-build:gcc --cxxopt -Wno-error=sign-compare
+# These are copts because they apply to both c++ and c files.
+# In particular, upb is has issues with this that will hopefully be
+# fixed upstream soon.
+build:gcc --copt -Wno-error=sign-compare
+build:gcc --copt -Wno-error=stringop-truncation
+build:gcc --copt -Wno-error=maybe-uninitialized
 
 # Default build opts:
 build --config=clang

bazel/pl_build_system.bzl

@@ -27,7 +27,12 @@ def pl_copts():
 
     # Leaving this here as an example of how to add compiler dependent_flags.
     compiler_dependent_flags = select({
-        "@pl//bazel:gcc_build": [],
+        "@pl//bazel:gcc_build": [
+            # Since we globally disable these warnings in the .bazelrc file,
+            # we force them enabled for our own source code.
+            "-Werror=stringop-truncation",
+            "-Werror=maybe-uninitialized",
+        ],
         "//conditions:default": [
             # TODO(yzhao/oazizi): Please remove this after fixing warnings in stirling.
             "-Wno-c99-designator",