[ARM] Create relocations for beq.w branches to ARM function syms.

[fhahn]

Summary

The ARM ELF ABI requires the linker to do interworking for wide
conditional branches from Thumb code to ARM code.

That was pointed out by @peter.smith in the comments for D33436.

[peter.smith]

I'm happy with these changes, will be worth waiting a day or so to see if anyone else objects.

lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
   // different execution mode in ELF binaries.
   if (Sym && Sym->isELF()) {
     unsigned Type = dyn_cast<MCSymbolELF>(Sym)->getType();
     if ((Type == ELF::STT_FUNC || Type == ELF::STT_GNU_IFUNC)) {
       if (Asm.isThumbFunc(Sym) && (FixupKind == ARM::fixup_arm_uncondbranch))
         IsResolved = false;
       if (!Asm.isThumbFunc(Sym) && (FixupKind == ARM::fixup_arm_thumb_br ||
                                     FixupKind == ARM::fixup_arm_thumb_bl ||
+                                    FixupKind == ARM::fixup_t2_condbranch ||
                                     FixupKind == ARM::fixup_t2_uncondbranch))
         IsResolved = false;
     }
   }
   // We must always generate a relocation for BL/BLX instructions if we have
   // a symbol to reference, as the linker relies on knowing the destination
   // symbol's thumb-ness to get interworking right.
   if (A && (FixupKind == ARM::fixup_arm_thumb_blx ||

test/MC/ARM/thumb2-beq-fixup.s

+@ RUN: llvm-mc < %s -triple armv7-linux-gnueabi -filetype=obj -o - \
+@ RUN:   | llvm-readobj -r | FileCheck %s
+
+  .code  16
+  .thumb_func
+thumb_caller:
+  beq.w internal_arm_fn
+  beq.w global_arm_fn
+  beq.w global_thumb_fn
+  beq.w internal_thumb_fn
+
+  .type  internal_arm_fn,%function
+  .code  32
+internal_arm_fn:
+  bx  lr
+
+  .globl  global_arm_fn
+  .type  global_arm_fn,%function
+  .code  32
+global_arm_fn:
+  bx  lr
+
+  .type  internal_thumb_fn,%function
+  .code  16
+  .thumb_func
+internal_thumb_fn:
+  bx  lr
+
+  .globl  global_thumb_fn
+  .type  global_thumb_fn,%function
+  .code  16
+  .thumb_func
+global_thumb_fn:
+  bx  lr
+
+@ CHECK: Section (3) .rel.text
+@ CHECK-NEXT: 0x0 R_ARM_THM_JUMP19 internal_arm_fn 0x0
+@ CHECK-NEXT: 0x4 R_ARM_THM_JUMP19 global_arm_fn 0x0
+@ CHECK-NEXT: }