Remove -Wa,noexecstack from unsupported arm clang flags

This was marked as unsupported only on arm[64], even though it works.
For soong, we want to keep a single list of unsupported clang flags
for all architectures.

Change-Id: I9c4ae0f255c549d2346ba7abae57e22c86ddcc61

core/clang/arm.mk

@@ -29,8 +29,7 @@ CLANG_CONFIG_arm_UNKNOWN_CFLAGS := \
   -fno-partial-inlining \
   -fno-strict-volatile-bitfields \
   -fno-tree-copy-prop \
-  -fno-tree-loop-optimize \
-  -Wa,--noexecstack
+  -fno-tree-loop-optimize
 
 define subst-clang-incompatible-arm-flags
   $(subst -march=armv5te,-march=armv5t,\

core/clang/arm64.mk

@@ -13,8 +13,7 @@ CLANG_CONFIG_arm64_UNKNOWN_CFLAGS := \
   -frerun-cse-after-loop \
   -frename-registers \
   -fno-strict-volatile-bitfields \
-  -fno-align-jumps \
-  -Wa,--noexecstack
+  -fno-align-jumps
 
 # We don't have any arm64 flags to substitute yet.
 define subst-clang-incompatible-arm64-flags