tests

build(CMake): Require C99 mode #1002

Job	Run time
C Makefile tests	1m 40s
build with the Tiny C Compiler	8s
build for Apple Silicon	1m 5s
b3sum Linux GNU stable	14s
b3sum Linux GNU beta	22s
CMake ubuntu-latest gcc	16s
b3sum Linux GNU nightly	26s
cross i586-unknown-linux-musl	1m 36s
CMake ubuntu-latest clang	14s
compile and test with GCC 5.4	1m 7s
b3sum Linux GNU 1.70.0	29s
cross i686-unknown-linux-musl	1m 41s
CMake ubuntu-latest cl	5s
b3sum macOS stable	51s
cross armv7-unknown-linux-gnueabihf	1m 36s
CMake macOS-latest gcc	14s
b3sum macOS beta	36s
cross aarch64-unknown-linux-gnu	1m 45s
b3sum macOS nightly	33s
CMake macOS-latest clang	12s
cross powerpc64-unknown-linux-gnu	1m 31s
b3sum macOS 1.70.0	46s
Linux GNU stable	2m 28s
CMake macOS-latest cl	12s
cross s390x-unknown-linux-gnu	1m 43s
b3sum Windows MSVC stable	1m 48s
Linux GNU beta	2m 24s
CMake windows-latest clang	1m 0s
b3sum Windows MSVC beta	56s
Linux GNU nightly	2m 23s
CMake windows-latest cl	1m 25s
b3sum Windows MSVC nightly	47s
Linux GNU 1.66.1	6m 32s
b3sum Windows MSVC 1.70.0	1m 1s
macOS stable	7m 14s
b3sum Windows GNU stable	1m 11s
macOS beta	3m 20s
macOS nightly	3m 23s
b3sum Windows GNU beta	1m 12s
macOS 1.66.1	9m 21s
b3sum Windows GNU nightly	1m 12s
Windows MSVC stable	4m 22s
b3sum Windows GNU 1.70.0	1m 13s
Windows MSVC beta	4m 26s
Windows MSVC nightly	4m 36s
Windows MSVC 1.66.1	9m 25s
Windows GNU stable	5m 5s
Windows GNU beta	4m 37s
Windows GNU nightly	4m 41s
Windows GNU 1.66.1	9m 50s
	1h 55m 14s

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