cc: Enable select syntax for cppflags

Bug: 325444956
Test: m
Test: m [custom build target with select in cppflags]
Change-Id: I7d27096526ce5b37afe447f900613a6fbb639986
diff --git a/cc/compiler.go b/cc/compiler.go
index 03f9899..ed10533 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -53,7 +53,7 @@
 	Cflags proptools.Configurable[[]string] `android:"arch_variant"`
 
 	// list of module-specific flags that will be used for C++ compiles
-	Cppflags []string `android:"arch_variant"`
+	Cppflags proptools.Configurable[[]string] `android:"arch_variant"`
 
 	// list of module-specific flags that will be used for C compiles
 	Conlyflags []string `android:"arch_variant"`
@@ -367,8 +367,9 @@
 	compiler.srcsBeforeGen = append(compiler.srcsBeforeGen, deps.GeneratedSources...)
 
 	cflags := compiler.Properties.Cflags.GetOrDefault(ctx, nil)
+	cppflags := compiler.Properties.Cppflags.GetOrDefault(ctx, nil)
 	CheckBadCompilerFlags(ctx, "cflags", cflags)
-	CheckBadCompilerFlags(ctx, "cppflags", compiler.Properties.Cppflags)
+	CheckBadCompilerFlags(ctx, "cppflags", cppflags)
 	CheckBadCompilerFlags(ctx, "conlyflags", compiler.Properties.Conlyflags)
 	CheckBadCompilerFlags(ctx, "asflags", compiler.Properties.Asflags)
 	CheckBadCompilerFlags(ctx, "vendor.cflags", compiler.Properties.Target.Vendor.Cflags)
@@ -381,7 +382,7 @@
 	esc := proptools.NinjaAndShellEscapeList
 
 	flags.Local.CFlags = append(flags.Local.CFlags, esc(cflags)...)
-	flags.Local.CppFlags = append(flags.Local.CppFlags, esc(compiler.Properties.Cppflags)...)
+	flags.Local.CppFlags = append(flags.Local.CppFlags, esc(cppflags)...)
 	flags.Local.ConlyFlags = append(flags.Local.ConlyFlags, esc(compiler.Properties.Conlyflags)...)
 	flags.Local.AsFlags = append(flags.Local.AsFlags, esc(compiler.Properties.Asflags)...)
 	flags.Local.YasmFlags = append(flags.Local.YasmFlags, esc(compiler.Properties.Asflags)...)
@@ -808,7 +809,7 @@
 
 	// list of c++ specific clang flags required to correctly interpret the headers.
 	// This is provided primarily to make sure cppflags defined in cc_defaults are pulled in.
-	Cppflags []string `android:"arch_variant"`
+	Cppflags proptools.Configurable[[]string] `android:"arch_variant"`
 
 	// C standard version to use. Can be a specific version (such as "gnu11"),
 	// "experimental" (which will use draft versions like C1x when available),