Use `IMPORTED` OpenGL target #104

Job	Run time
clang-format	15s
Windows MSVC Shared Release	2m 17s
Windows MSVC Shared Debug	2m 11s
Windows MSVC Static Release	2m 46s
Windows MSVC Static Debug	2m 29s
Windows ClangCL Shared Release	5m 3s
Windows ClangCL Shared Debug	3m 23s
Windows ClangCL Static Release	4m 18s
Windows ClangCL Static Debug	4m 49s
Windows MinGW Shared Release	4m 34s
Windows MinGW Shared Debug	2m 16s
Windows MinGW Static Release	2m 30s
Windows MinGW Static Debug	2m 30s
Linux GCC Shared Release	1m 6s
Linux GCC Shared Debug	1m 4s
Linux GCC Static Release	1m 54s
Linux GCC Static Debug	49s
Linux Clang Shared Release	1m 47s
Linux Clang Shared Debug	59s
Linux Clang Static Release	1m 8s
Linux Clang Static Debug	1m 5s
macOS Xcode Shared Release	2m 23s
macOS Xcode Shared Debug	2m 17s
macOS Xcode Static Release	2m 48s
macOS Xcode Static Debug	2m 19s
	59m 0s

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