Refactor llvm_config.mk and support the 2nd arch

1. Following the setup of gcc in build/core/combo/,
we added the [HOST|TARGET]_<arch>.mk clang config files,
and load only the configs needed by the current product.
2. Added support for the 2nd arch.

Change-Id: I2a383418a9688a050b39492f8e489d40eeeb5f2d
diff --git a/core/clang/mips.mk b/core/clang/mips.mk
new file mode 100644
index 0000000..cef7823
--- /dev/null
+++ b/core/clang/mips.mk
@@ -0,0 +1,28 @@
+# Clang flags for mips arch, target or host.
+
+CLANG_CONFIG_mips_EXTRA_ASFLAGS :=
+CLANG_CONFIG_mips_EXTRA_CFLAGS :=
+CLANG_CONFIG_mips_EXTRA_LDFLAGS :=
+
+# Include common unknown flags
+CLANG_CONFIG_mips_UNKNOWN_CFLAGS := \
+  $(CLANG_CONFIG_UNKNOWN_CFLAGS) \
+  -EL \
+  -mips32 \
+  -mips32r2 \
+  -mhard-float \
+  -fno-strict-volatile-bitfields \
+  -fgcse-after-reload \
+  -frerun-cse-after-loop \
+  -frename-registers \
+  -march=mips32r2 \
+  -mtune=mips32r2 \
+  -march=mips32 \
+  -mtune=mips32 \
+  -msynci \
+  -mno-fused-madd
+
+# We don't have any mips flags to substitute yet.
+define subst-clang-incompatible-mips-flags
+  $(1)
+endef