build-kernel.sh: Use GCC 4.9 automatically for Mips64 build.

+ Fix the auto-generated README file to mention "mips64" instead
  of "mips".

Change-Id: I2fecb008398979612f440271a028921900311f78
diff --git a/build-kernel.sh b/build-kernel.sh
index a8a85aa..beb5984 100755
--- a/build-kernel.sh
+++ b/build-kernel.sh
@@ -168,6 +168,9 @@
         # There is no GCC 4.7 toolchain to build AARCH64 binaries.
         GCC_VERSION=4.8
     fi
+    if [ "$ARCH" = "mips64" ]; then
+        GCC_VERSION=4.9
+    fi
     echo "Autoconfig: --gcc-version=$GCC_VERSION"
 fi
 
@@ -357,6 +360,7 @@
         ;;
 esac
 
+ORG_ARCH=$ARCH
 case $ARCH in
     mips64)
         # MIPS64 Kernel code base is under arch/mips
@@ -419,7 +423,7 @@
 
 cat > $OUTPUT/README <<EOF
 This directory contains kernel images to be used with the Android emulator
-program, for the $ARCH CPU architecture. It was built with the $PROGNAME
+program, for the $ORG_ARCH CPU architecture. It was built with the $PROGNAME
 script. For more details, read:
 
   \$AOSP/external/qemu/docs/ANDROID-KERNEL.TXT