When building with bazel on a Mac, workaround bazelbuild/bazel#4341

include/grpc/impl/codegen/port_platform.h

@@ -195,12 +195,25 @@
 #define GPR_PTHREAD_TLS 1
 #else /* __MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_7 */
 #define GPR_CPU_POSIX 1
+/* TODO(vjpai): there is a reported issue in bazel build for Mac where __thread
+   in a header is currently not working (bazelbuild/bazel#4341). Remove
+   the following conditional and use GPR_GCC_TLS when that is fixed */
+#ifndef GRPC_BAZEL_BUILD
 #define GPR_GCC_TLS 1
+#else /* GRPC_BAZEL_BUILD */
+#define GPR_PTHREAD_TLS 1
+#endif /* GRPC_BAZEL_BUILD */
 #define GPR_APPLE_PTHREAD_NAME 1
 #endif
 #else /* __MAC_OS_X_VERSION_MIN_REQUIRED */
 #define GPR_CPU_POSIX 1
+/* TODO(vjpai): Remove the following conditional and use only GPR_GCC_TLS
+   when bazelbuild/bazel#4341 is fixed */
+#ifndef GRPC_BAZEL_BUILD
 #define GPR_GCC_TLS 1
+#else /* GRPC_BAZEL_BUILD */
+#define GPR_PTHREAD_TLS 1
+#endif /* GRPC_BAZEL_BUILD */
 #endif
 #define GPR_POSIX_CRASH_HANDLER 1
 #endif

tools/bazel.rc

@@ -1,4 +1,5 @@
 build --client_env=CC=clang
+build --copt -DGRPC_BAZEL_BUILD
 
 build:asan --strip=never
 build:asan --copt -fsanitize-coverage=edge