[llvm-cov] NFC: Specify a specific C++ standard in the test.
Makes life easier for downstream users with customized default standard.
// 1) Compile shared code into different object files and into an executable.
-// RUN: %clangxx_profgen -fcoverage-mapping %s -c -o %t.v1.o -D_VERSION_1
-// RUN: %clangxx_profgen -fcoverage-mapping %s -c -o %t.v2.o -D_VERSION_2
-// RUN: %clangxx_profgen -fcoverage-mapping %t.v1.o %t.v2.o -o %t.exe
+// RUN: %clangxx_profgen -std=c++14 -fcoverage-mapping %s -c -o %t.v1.o \
+// RUN: -D_VERSION_1
+// RUN: %clangxx_profgen -std=c++14 -fcoverage-mapping %s -c -o %t.v2.o \
+// RUN: -D_VERSION_2
+// RUN: %clangxx_profgen -std=c++14 -fcoverage-mapping %t.v1.o %t.v2.o \
+// RUN: -o %t.exe
// 2) Collect profile data.
