[CUDA] Make min/max shims host+device.
[CUDA] Make min/max shims host+device.

Summary:
Fixes PR37753: min/max can't be called from __host__ __device__
functions in C++14 mode.

Testcase in a separate test-suite commit.

Reviewers: rsmith

Subscribers: sanjoy, lahwaacz, cfe-commits

Differential Revision: https://reviews.llvm.org/D48036

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@336025 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang