Drop memory barriers from _aromic_lock() on armv7 and arm64

[Mark Kettenis]

Since the callers now add the barriers we can drop them here.

ok?


Index: lib/libc/arch/aarch64/gen/_atomic_lock.c
===================================================================
RCS file: /cvs/src/lib/libc/arch/aarch64/gen/_atomic_lock.c,v
retrieving revision 1.1
diff -u -p -r1.1 _atomic_lock.c
--- lib/libc/arch/aarch64/gen/_atomic_lock.c    15 Aug 2017 06:16:37 -0000      
1.1
+++ lib/libc/arch/aarch64/gen/_atomic_lock.c    14 May 2018 18:34:02 -0000
@@ -41,7 +41,6 @@ _atomic_lock(volatile _atomic_lock_t *lo
                "   stlxr %w2, %w3, [%x1]  \n"
                "   cmp %w2, #0            \n"
                "   bne 1b                 \n"
-               "   dmb sy                 \n"
                : "+r" (old), "+r" (lock), "+r" (scratch)
                : "r" (_ATOMIC_LOCK_LOCKED));
 
Index: lib/libc/arch/arm/gen/_atomic_lock.c
===================================================================
RCS file: /cvs/src/lib/libc/arch/arm/gen/_atomic_lock.c,v
retrieving revision 1.1
diff -u -p -r1.1 _atomic_lock.c
--- lib/libc/arch/arm/gen/_atomic_lock.c        15 Aug 2017 06:13:24 -0000      
1.1
+++ lib/libc/arch/arm/gen/_atomic_lock.c        14 May 2018 18:34:02 -0000
@@ -41,7 +41,6 @@ _atomic_lock(volatile _atomic_lock_t *lo
                "   strex %2, %3, [%1]  \n"
                "   cmp %2, #0          \n"
                "   bne 1b              \n"
-               "   dmb sy              \n"
                : "+r" (old), "+r" (lock), "+r" (scratch)
                : "r" (_ATOMIC_LOCK_LOCKED));