Put jump tables in unique sections on COFF.

Put jump tables in unique sections on COFF.

If a function is going in an unique section (because of -ffunction-sections
for example), putting a jump table in .rodata will keep .rodata alive and
that will keep alive any other function that also has a jump table.

Instead, put the jump table in a unique section that is associated with the
function.

llvm-svn: 231961