Set the compiler via the environment #615

Job	Run time
Docs	25s
Coverage	58s
clang-format	44s
Windows MSVC Shared Debug	2m 42s
ASan	53s
clang-tidy	1m 3s
UBSan	51s
Windows MSVC Shared Release	2m 6s
Windows MSVC Static Debug	2m 31s
Windows MSVC Static Release	2m 33s
Windows ClangCL Shared Debug	2m 43s
Windows ClangCL Shared Release	2m 9s
Windows ClangCL Static Debug	3m 7s
Windows ClangCL Static Release	3m 42s
Windows Clang Shared Debug	2m 32s
Windows Clang Shared Release	3m 18s
Windows Clang Static Debug	2m 51s
Windows Clang Static Release	2m 48s
Linux GCC Shared Debug	54s
Linux GCC Shared Release	54s
Linux GCC Static Debug	58s
Linux GCC Static Release	49s
Linux Clang Shared Debug	49s
Linux Clang Shared Release	1m 10s
Linux Clang Static Debug	50s
Linux Clang Static Release	49s
macOS GCC Shared Debug	17s
macOS GCC Shared Release	21s
macOS GCC Static Debug	17s
macOS GCC Static Release	18s
macOS Clang Shared Debug	1m 49s
macOS Clang Shared Release	1m 50s
macOS Clang Static Debug	1m 37s
macOS Clang Static Release	2m 51s
	54m 29s

Provide feedback