Revert "Do not build art with clang for mips64"

This reverts commit 610a1420fe400d3f638fc0dadb1a012d2ac3ad19.

Bug: 25928358
Change-Id: I3fe8777ead2bd067c071277a7c15b2442f15567f
diff --git a/build/Android.common_build.mk b/build/Android.common_build.mk
index dc53853..02bce41 100644
--- a/build/Android.common_build.mk
+++ b/build/Android.common_build.mk
@@ -118,8 +118,7 @@
 ART_TARGET_CLANG_arm := false
 ART_TARGET_CLANG_arm64 :=
 ART_TARGET_CLANG_mips :=
-# b/25928358, illegal instruction on mips64r6 with -O0
-ART_TARGET_CLANG_mips64 := false
+ART_TARGET_CLANG_mips64 :=
 ART_TARGET_CLANG_x86 :=
 ART_TARGET_CLANG_x86_64 :=