Automatically set QUICHE --config=macos on macOS

https://bazel.build/reference/command-line-reference#flag--enable_platform_specific_config

This change does not impact any production systems.

PiperOrigin-RevId: 569552720

.bazelrc

diff --git a/.bazelrc b/.bazelrc
index dda6d24..3b2dcc0 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -1,3 +1,6 @@
+# Automatically detect host platform to pick config
+common --enable_platform_specific_config
+
 build --cxxopt=-std=c++17
 build --cxxopt=-fno-rtti