Merging r370176:

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r370176 | hans | 2019-08-28 11:21:56 +0200 (Wed, 28 Aug 2019) | 15 lines

[LLVM-C] Fix ByVal Attribute crashing

With the introduction of the typed byval attribute change there was no
way that the LLVM-C API could create the correct class Attribute. If a
program that uses the C API creates a ByVal attribute and annotates a
function with that attribute LLVM will crash when it assembles or write
that module containing the function out as bitcode.

This change is a minimal fix to at least allow code to work, this is
because the byval change is on the 9.0 and I don't want to introduce new
LLVM-C API this late in the release cycle.

By Jakob Bornecrantz!

Differential revision: https://reviews.llvm.org/D66144
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llvm-svn: 370178