ARMv7 SIMD: Fix clang compatibility (Part 2)

GCC does support UAL syntax (strbeq) if the ".syntax unified" directive
is supplied.  This directive is supported by all versions of GCC and
clang going back to 2003, so it should not create any backward
compatibility issues.

Based on https://github.com/mattsarett/libjpeg-turbo/commit/1264349e2fa6f098178c37abfa7b059ad8b405a2

Closes #76

simd/jsimd_arm_neon.S

diff --git a/simd/jsimd_arm_neon.S b/simd/jsimd_arm_neon.S
index 06b7240..568768f 100644
--- a/simd/jsimd_arm_neon.S
+++ b/simd/jsimd_arm_neon.S
@@ -35,6 +35,7 @@
 .arch armv7a
 .object_arch armv4
 .arm
+.syntax unified
 
 
 #define RESPECT_STRICT_ALIGNMENT 1
@@ -2457,11 +2458,7 @@
     strb            \TMP, [\BUFFER, #1]!
     cmp             \TMP, #0xff
     /*it eq*/
-#if defined(__clang__)
     strbeq          \ZERO, [\BUFFER, #1]!
-#else
-    streqb          \ZERO, [\BUFFER, #1]!
-#endif
 .endm
 
 .macro put_bits PUT_BUFFER, PUT_BITS, CODE, SIZE