treewide: make public headers compile with c89/c99/c11 pedantic errors #4089

Job	Run time
Build mlibc (x86_64, mlibc, gcc)	2m 7s
Compile sysdeps (dripos)	2m 17s
Build mlibc (x86_64, mlibc-static, gcc)	1s
Compile sysdeps (lemon)	2m 22s
Build mlibc (x86_64, mlibc-shared, gcc)	1s
Build mlibc (x86_64, mlibc-ansi-only, gcc)	2m 6s
Build mlibc (x86_64, mlibc-headers-only, gcc)	1s
Compile sysdeps (aero)	2m 15s
Build mlibc (riscv64, mlibc, gcc)	2m 8s
Compile sysdeps (ironclad)	2m 22s
Build mlibc (riscv64, mlibc-static, gcc)	2m 7s
Compile sysdeps (lyre)	2m 16s
Build mlibc (riscv64, mlibc-shared, gcc)	2m 6s
Compile sysdeps (keyronex)	2m 27s
Build mlibc (riscv64, mlibc-ansi-only, gcc)	2m 7s
Compile sysdeps (managarm)	2m 32s
Build mlibc (riscv64, mlibc-headers-only, gcc)	2m 1s
Compile sysdeps (vinix)	2m 19s
Build mlibc (aarch64, mlibc, gcc)	2m 7s
Compile sysdeps (astral)	2m 21s
Build mlibc (aarch64, mlibc-static, gcc)	2m 5s
Build mlibc (aarch64, mlibc-shared, gcc)	2m 8s
Build mlibc (aarch64, mlibc-ansi-only, gcc)	2m 8s
Build mlibc (aarch64, mlibc-headers-only, gcc)	2m 8s
Build mlibc (x86, mlibc, gcc)	1s
Build mlibc (x86, mlibc-static, gcc)	1s
Build mlibc (x86, mlibc-shared, gcc)	1s
Build mlibc (x86, mlibc-ansi-only, gcc)	1s
Build mlibc (x86, mlibc-headers-only, gcc)	1s
Build mlibc (m68k, mlibc, gcc)	2m 8s
Build mlibc (m68k, mlibc-static, gcc)	2m 7s
Build mlibc (m68k, mlibc-shared, gcc)	2m 4s
Build mlibc (m68k, mlibc-ansi-only, gcc)	2m 8s
Build mlibc (m68k, mlibc-headers-only, gcc)	1m 59s
Build mlibc (x86_64, mlibc, clang)	2m 8s
	59m 11s

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