Revert "Update clang version to clang-r475365"

This reverts commit 7a53b71f3ba020f354b31cd75a8714291fdb5cb2.

Reason for revert: fix aosp_riscv64-userdebug build

Change-Id: Ie1579c5692335573b85fd5b062a4104023276287
diff --git a/cc/config/global.go b/cc/config/global.go
index ab26c78..e5c0a8e 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -243,10 +243,6 @@
 		"-Wno-error=array-parameter",     // http://b/241941550
 		"-Wno-error=deprecated-builtins", // http://b/241601211
 		"-Wno-error=deprecated",          // in external/googletest/googletest
-		// New warnings to be fixed after clang-r475365
-		"-Wno-error=single-bit-bitfield-constant-conversion", // http://b/243965903
-		"-Wno-error=incompatible-function-pointer-types",     // http://b/257101299
-		"-Wno-error=enum-constexpr-conversion",               // http://b/243964282
 	}
 
 	noOverrideExternalGlobalCflags = []string{
@@ -296,6 +292,8 @@
 	llvmNextExtraCommonGlobalCflags = []string{
 		// New warnings to be fixed after clang-r475365
 		"-Wno-error=single-bit-bitfield-constant-conversion", // http://b/243965903
+		// Skip deprecated flags.
+		"-Wno-unused-command-line-argument",
 	}
 
 	IllegalFlags = []string{
@@ -309,8 +307,8 @@
 
 	// prebuilts/clang default settings.
 	ClangDefaultBase         = "prebuilts/clang/host"
-	ClangDefaultVersion      = "clang-r475365"
-	ClangDefaultShortVersion = "16.0.1"
+	ClangDefaultVersion      = "clang-r468909b"
+	ClangDefaultShortVersion = "15.0.3"
 
 	// Directories with warnings from Android.bp files.
 	WarningAllowedProjects = []string{
@@ -351,7 +349,6 @@
 			// Default to zero initialization.
 			"-ftrivial-auto-var-init=zero",
 			"-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang",
-			"-Wno-unused-command-line-argument",
 		}...)
 	exportedVars.ExportStringList("CommonGlobalCflags", bazelCommonGlobalCflags)
 
@@ -362,14 +359,14 @@
 		// Automatically initialize any uninitialized stack variables.
 		// Prefer zero-init if multiple options are set.
 		if ctx.Config().IsEnvTrue("AUTO_ZERO_INITIALIZE") {
-			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang -Wno-unused-command-line-argument")
+			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang")
 		} else if ctx.Config().IsEnvTrue("AUTO_PATTERN_INITIALIZE") {
 			flags = append(flags, "-ftrivial-auto-var-init=pattern")
 		} else if ctx.Config().IsEnvTrue("AUTO_UNINITIALIZE") {
 			flags = append(flags, "-ftrivial-auto-var-init=uninitialized")
 		} else {
 			// Default to zero initialization.
-			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang -Wno-unused-command-line-argument")
+			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang")
 		}
 
 		// Workaround for ccache with clang.