Decouple platform compiler and NDK library versioning.

TARGET_GCC_VERSION: select compiler from prebuilts/gcc/...
TARGET_NDK_GCC_VERSION: select libraries from prebuilts/ndk/...

Change-Id: I4422a42cdc97aa92b40798014cba82c3c123bbd2
diff --git a/core/combo/TARGET_linux-mips64.mk b/core/combo/TARGET_linux-mips64.mk
index 118582b..36b70ad 100644
--- a/core/combo/TARGET_linux-mips64.mk
+++ b/core/combo/TARGET_linux-mips64.mk
@@ -34,6 +34,9 @@
 TARGET_ARCH_VARIANT := mips64r2
 endif
 
+# Decouple NDK library selection with platform compiler version
+TARGET_NDK_GCC_VERSION := 4.8
+
 ifeq ($(strip $(TARGET_GCC_VERSION_EXP)),)
 TARGET_GCC_VERSION := 4.8
 else