Set the compiler via the environment #617

Job	Run time
clang-format	48s
Docs	8s
Coverage	56s
ASan	56s
Windows MSVC Shared Debug	1s
UBSan	1m 6s
clang-tidy	1m 5s
Windows MSVC Shared Release	1s
Windows MSVC Static Debug	1s
Windows MSVC Static Release	1s
Windows ClangCL Shared Debug	1s
Windows ClangCL Shared Release	1s
Windows ClangCL Static Debug	1s
Windows ClangCL Static Release	1s
Windows Clang Shared Debug	1s
Windows Clang Shared Release	1s
Windows Clang Static Debug	1s
Windows Clang Static Release	1s
Linux GCC Shared Debug	1s
Linux GCC Shared Release	1s
Linux GCC Static Debug	1s
Linux GCC Static Release	1s
Linux Clang Shared Debug	1s
Linux Clang Shared Release	1s
Linux Clang Static Debug	1s
Linux Clang Static Release	1s
macOS GCC Shared Debug	1s
macOS GCC Shared Release	1s
macOS GCC Static Debug	1s
macOS GCC Static Release	1s
macOS Clang Shared Debug	1s
macOS Clang Shared Release	1s
macOS Clang Static Debug	1s
macOS Clang Static Release	1s
	5m 27s

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