Fix include order

Include order should be module includes, dependency exported includes,
and then global includes.  Module includes and global includes are
computed during compileFlags, but dependency exported includes are
not handled until later.  Move the global includes into a new
flags variable so that the dependency includes can be appended
to the module includes.

Test: m -j native
Change-Id: Ifc3894f0a898a070d6da8eed4f4b9e8cc0cd2523

cc/cc.go

@@ -109,6 +109,10 @@ type Flags struct {
 	TidyFlags   []string // Flags that apply to clang-tidy
 	YasmFlags   []string // Flags that apply to yasm assembly source files
 
+	// Global include flags that apply to C, C++, and assembly source files
+	// These must be after any module include flags, which will be in GlobalFlags.
+	SystemIncludeFlags []string
+
 	Toolchain config.Toolchain
 	Clang     bool
 	Tidy      bool