Apply some tweaks to support MacOS 12.

  - Add GitHub CI build for macos-12.
  - `.bazelrc`: Configure `macos_minimum_os` to prompt correct toolchain selection for users with a complicated xcode configuration.
  - Addresses [#4](#4) regarding minimum MacOS version.
  - Also, fix [#8](#8) for MacOS 12.

PiperOrigin-RevId: 641012154

.bazelrc

@@ -5,3 +5,6 @@ build --cxxopt=-Wno-sign-compare
 # build.
 build --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
 build --enable_bzlmod=false
+
+# Platform specific configuration.
+build:macos --macos_minimum_os=12.0

.github/workflows/ci.yml

@@ -17,3 +17,10 @@ jobs:
         uses: actions/checkout@v4
       - name: Build
         uses: ./.github/actions/iamf-tools-builder
+  macos-amd64:
+    runs-on: macos-12
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+      - name: Build
+        uses: ./.github/actions/iamf-tools-builder

iamf/common/write_bit_buffer.cc

@@ -12,7 +12,6 @@
 #include "iamf/common/write_bit_buffer.h"
 
 #include <algorithm>
-#include <bit>
 #include <cstdint>
 #include <fstream>
 #include <iterator>
@@ -180,7 +179,7 @@ absl::Status WriteBitBuffer::WriteString(const std::string& data) {
   for (int i = 0; i < kIamfMaxStringSize; i++) {
     // Note that some systems have `char` as signed and others unsigned. Write
     // the same raw byte value regardless.
-    const uint8_t byte = std::bit_cast<uint8_t>(data[i]);
+    const uint8_t byte = static_cast<uint8_t>(data[i]);
     RETURN_IF_NOT_OK(WriteUnsignedLiteral(byte, 8));
 
     // Exit successfully after last byte was written.