[opaque pointers] Avoid the use of pointee types when parsing inline asm in IR

When parsing calls to inline asm the pointee type (of the pointer type
representing the value type of the InlineAsm value) was used. To avoid
using it, use the ValID structure to ferry the FunctionType directly
through to the InlineAsm construction.

This is a bit of a workaround - alternatively the inline asm could
explicitly describe the type but that'd be verbose/redundant in the IR
and so long as the inline asm calls directly in the context of a call or
invoke, this should suffice.

llvm-svn: 243349