[Builtins][ARM] Force ARM state for bswap for pre-ARMv6

[weimingz]

Summary

The instructions for bswp guarded by "__ARM_ARCH < 6" is ARM code. E.g., bic (immediate), eor (register-shifted register).
This patch forces ARM state even if -mthumb is used (e.g. -mthumb is passed as a global option by build system)

[efriedma]

lib/builtins/arm/bswapdi2.S

30

This doesn't do the right thing: the function symbol will still be decorated with .thumb_func, so this will try to execute ARM instructions in Thumb mode (and probably crash).

[weimingz]

guard the "DEFINE_CODE_STATE" with "__ARM_ARCH < 6" check.

lib/builtins/arm/bswapdi2.S

 //===------- bswapdi2 - Implement bswapdi2 --------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "../assembly.h"
 
   .syntax unified
   .text
+#if __ARM_ARCH < 6
+  .arm
+#else
   DEFINE_CODE_STATE
+#endif
 
 //
 // extern uint64_t __bswapdi2(uint64_t);
 //
 // Reverse all the bytes in a 64-bit integer.
 //
   .p2align 2
 DEFINE_COMPILERRT_FUNCTION(__bswapdi2)
 #if __ARM_ARCH < 6
     // before armv6 does not have "rev" instruction
     // r2 = rev(r0)
     eor r2, r0, r0, ror #16
     bic r2, r2, #0xff0000
     mov r2, r2, lsr #8
     eor r2, r2, r0, ror #8
     // r0 = rev(r1)
     eor r0, r1, r1, ror #16
     bic r0, r0, #0xff0000
     mov r0, r0, lsr #8
     eor r0, r0, r1, ror #8

lib/builtins/arm/bswapsi2.S

 //===------- bswapsi2 - Implement bswapsi2 --------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "../assembly.h"
 
   .syntax unified
   .text
+#if __ARM_ARCH < 6
+  .arm
+#else
   DEFINE_CODE_STATE
+#endif
 
 //
 // extern uint32_t __bswapsi2(uint32_t);
 //
 // Reverse all the bytes in a 32-bit integer.
 //
   .p2align 2
 DEFINE_COMPILERRT_FUNCTION(__bswapsi2)