Revert "Revert "Fast ART x86 interpreter""

This reverts commit 2d093a1213cc2f85b5e5e02782332657c479eb94.

Disable x86 mterp compilation on Mac host builds (but keep enabled
for all target builds).

Change-Id: Ie355279f166d2964a786646ee53f065b7e0f5ede
diff --git a/runtime/interpreter/mterp/x86/fpcvt.S b/runtime/interpreter/mterp/x86/fpcvt.S
new file mode 100644
index 0000000..7808285
--- /dev/null
+++ b/runtime/interpreter/mterp/x86/fpcvt.S
@@ -0,0 +1,17 @@
+%default {"instr":"","load":"","store":"","wide":"0"}
+/*
+ * Generic 32-bit FP conversion operation.
+ */
+    /* unop vA, vB */
+    movzbl  rINSTbl, %ecx                   # ecx <- A+
+    sarl    $$4, rINST                      # rINST <- B
+    $load   VREG_ADDRESS(rINST)             # %st0 <- vB
+    andb    $$0xf, %cl                      # ecx <- A
+    $instr
+    $store  VREG_ADDRESS(%ecx)              # vA <- %st0
+    .if $wide
+    CLEAR_WIDE_REF %ecx
+    .else
+    CLEAR_REF %ecx
+    .endif
+    ADVANCE_PC_FETCH_AND_GOTO_NEXT 1