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

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.

Reviewers: rafael, peter.smith, echristo

Reviewed By: peter.smith

Subscribers: aemerson, javed.absar, kristof.beyls, llvm-commits, peter.smith

Differential Revision: https://reviews.llvm.org/D34447

llvm-svn: 306009