ARM: 8851/1: add TUSERCOND() macro for conditional postfix

ARM: 8851/1: add TUSERCOND() macro for conditional postfix

Unified assembly syntax requires conditionals to be postfixes.
TUSER() currently only takes a single argument which then gets
appended t (with translation) on every instruction.

This fixes a build error when using LLVM's integrated assembler:
  In file included from kernel/futex.c:72:
  ./arch/arm/include/asm/futex.h:116:3: error: invalid instruction, did you mean: strt?
          "2:     " TUSER(streq) "        %3, [%4]n"
           ^
  <inline asm>:5:4: note: instantiated into assembly here
  2:      streqt  r2, [r4]
          ^~~~~~

Additionally, for GCC ".syntax unified" for inline assembly.
When compiling non-Thumb2 GCC always emits a ".syntax divided"
at the beginning of the inline assembly which makes the
assembler fail. Since GCC 5 there is the -masm-syntax-unified
GCC option which make GCC assume unified syntax asm and hence
emits ".syntax unified" even in ARM mode. However, the option
is broken since GCC version 6 (see GCC PR88648 [1]). Work
around by adding ".syntax unified" as part of the inline
assembly.

[0] https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html#index-masm-syntax-unified
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>