rust: Pass additional Clang C flags from toolchain

The set of Clang flags passed to bindgen from the toolchain was
incomplete. In addition to ToolchainClangCflags(), we also need to call
ClangCflags().

Bug: 184081465
Test: m libgrpc_bindgen
Change-Id: I0b62345fee2f55ba18b4a0c4d825f0447c99db06

rust/bindgen.go

@@ -144,6 +144,7 @@ func (b *bindgenDecorator) GenerateSource(ctx ModuleContext, deps PathDeps) andr
 
 	// Toolchain clang flags
 	cflags = append(cflags, "-target "+ccToolchain.ClangTriple())
+	cflags = append(cflags, strings.ReplaceAll(ccToolchain.ClangCflags(), "${config.", "${cc_config."))
 	cflags = append(cflags, strings.ReplaceAll(ccToolchain.ToolchainClangCflags(), "${config.", "${cc_config."))
 
 	// Dependency clang flags and include paths