Merging r354074:

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r354074 | epilk | 2019-02-14 23:48:01 +0100 (Thu, 14 Feb 2019) | 9 lines

[Sema] Fix-up a -Wfloat-conversion diagnostic

We were warning on valid ObjC property reference exprs, and passing
in the wrong arguments to DiagnoseFloatingImpCast (leading to a badly
worded diagnostic).

rdar://47644670

Differential revision: https://reviews.llvm.org/D58145
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llvm-svn: 354129