ARM: 9022/1: Change arch/arm/lib/mem*.S to use WEAK instead of .weak

Commit d6d51a96 ("ARM: 9014/2: Replace string mem* functions for
KASan") add .weak directives to memcpy/memmove/memset to avoid collision
with KASAN interceptors.

This does not work with LLVM's integrated assembler (the assembly snippet
`.weak memcpy ... .globl memcpy` produces a STB_GLOBAL memcpy while GNU as
produces a STB_WEAK memcpy). LLVM 12 (since https://reviews.llvm.org/D90108)
will error on such an overridden symbol binding.

Use the appropriate WEAK macro instead.

Link: https://github.com/ClangBuiltLinux/linux/issues/1190


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Fixes: d6d51a96 ("ARM: 9014/2: Replace string mem* functions for KASan")
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>