[PR37339] Fix assertion in FunctionComparator::cmpInlineAsm

Fixes bug https://bugs.llvm.org/show_bug.cgi?id=37339.

InlineAsm is only uniqued if the FunctionTypes are exactly the
same, while cmpTypes() for example considers all pointer types
in the default address space to be the same. For this reason
the end of cmpInlineAsm() can be reached.

This patch replaces the unreachable assertion with a check that
the function types are not identical.

Differential Revision: https://reviews.llvm.org/D46495

Reviewers: jfb
llvm-svn: 331990