[OpenMP][AArch64] Fix compile with LLVM trunk.

The code is currently using the ambiguous instruction
"sub sp, sp, w9, lsl #4". The ARM reference manual says this isn't
valid, and it's not clear whether it's supposed to mean uxtw or uxtx.

It doesn't matter which instruction we use here, since the high
bits of the operand are zero anyway, so I arbitrarily choose uxtw, to
preserve the register name.

See https://reviews.llvm.org/D60840 for the LLVM patch.

Differential Revision: https://reviews.llvm.org/D61770



git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@360711 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/runtime/src/z_Linux_asm.S b/runtime/src/z_Linux_asm.S
index 1197864..39bf427 100644
--- a/runtime/src/z_Linux_asm.S
+++ b/runtime/src/z_Linux_asm.S
@@ -1243,7 +1243,7 @@
 
 	orr	w9, wzr, #1
 	add	w9, w9, w3, lsr #1
-	sub	sp, sp, w9, lsl #4
+	sub	sp, sp, w9, uxtw #4
 	mov	x11, sp
 
 	mov	x8, x0