Try to bump the C default to C11.

Even the Linux kernel's moved, so let's see if we can too...

Test: treehugger
Change-Id: Ic8ceb3b6e7a83acc5defee46618a9345a366d87d

cc/cc_test.go

@@ -3980,7 +3980,7 @@ func TestIncludeDirectoryOrdering(t *testing.T) {
 	cppOnly := []string{"-fPIC", "${config.CommonGlobalCppflags}", "${config.DeviceGlobalCppflags}", "${config.ArmCppflags}"}
 
 	cflags := []string{"-Wall", "-Werror", "-std=candcpp"}
-	cstd := []string{"-std=gnu99", "-std=conly"}
+	cstd := []string{"-std=gnu11", "-std=conly"}
 	cppstd := []string{"-std=gnu++17", "-std=cpp", "-fno-rtti"}
 
 	lastIncludes := []string{

cc/config/global.go

@@ -280,7 +280,7 @@ var (
 		"-w",
 	}
 
-	CStdVersion               = "gnu99"
+	CStdVersion               = "gnu11"
 	CppStdVersion             = "gnu++17"
 	ExperimentalCStdVersion   = "gnu11"
 	ExperimentalCppStdVersion = "gnu++2a"