Refactor bionic includes into a single place

Bionic includes are the same on all architectures, modulo
architecture-specific includes.  Use a single function to populate the
list, passing in bionic's and the kernel's names for the architecture.

Also get rid of the ${LibcRoot} variable, it is not providing any value
and makes grepping harder.

Change-Id: I39e7907d312f52dd1378a3937ab1bcba12c4e97f
diff --git a/cc/toolchain.go b/cc/toolchain.go
index 2e2ee5a..89485f8 100644
--- a/cc/toolchain.go
+++ b/cc/toolchain.go
@@ -16,6 +16,7 @@
 
 import (
 	"fmt"
+	"strings"
 
 	"android/soong/android"
 )
@@ -139,3 +140,14 @@
 func (toolchain32Bit) Is64Bit() bool {
 	return false
 }
+
+func bionicHeaders(bionicArch, kernelArch string) string {
+	return strings.Join([]string{
+		"-isystem bionic/libc/arch-" + bionicArch + "/include",
+		"-isystem bionic/libc/include",
+		"-isystem bionic/libc/kernel/uapi",
+		"-isystem bionic/libc/kernel/android/uapi",
+		"-isystem bionic/libc/kernel/common",
+		"-isystem bionic/libc/kernel/uapi/asm-" + kernelArch,
+	}, " ")
+}