Compress debug info in clang builds with zstd

We can save a significant amount of disk space by compressing
debug info in `clang` builds. This change configures a build
flag to instruct clang to compress debug info.

Test: m
Bug: 305277519
Change-Id: Ieeaa655452d847e83ebc6bec0864e47c46f4c6fb
diff --git a/cc/config/global.go b/cc/config/global.go
index 62b008b..be81b2e 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -133,6 +133,9 @@
 		// Using simple template names reduces the size of debug builds.
 		"-gsimple-template-names",
 
+		// Use zstd to compress debug data.
+		"-gz=zstd",
+
 		// Make paths in deps files relative.
 		"-no-canonical-prefixes",
 	}