Merging r366481:

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r366481 | teemperor | 2019-07-18 20:33:40 +0200 (Thu, 18 Jul 2019) | 4 lines

Fix C++ modules build

llvm-svn: 366344 missed an include that broke the LLVM_ENABLE_MODULES
build.
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llvm-svn: 366757