treewide: make public headers compile with c89/c99/c11 pedantic errors #4080

Job	Run time
Build mlibc (x86_64, mlibc, gcc)	1s
Build mlibc (x86_64, mlibc-static, gcc)	1s
Compile sysdeps (dripos)	2m 11s
Build mlibc (x86_64, mlibc-shared, gcc)	1s
Compile sysdeps (lemon)	2m 21s
Build mlibc (x86_64, mlibc-ansi-only, gcc)	1s
Compile sysdeps (aero)	2m 26s
Build mlibc (x86_64, mlibc-headers-only, gcc)	1s
Compile sysdeps (ironclad)	2m 9s
Build mlibc (riscv64, mlibc, gcc)	18s
Compile sysdeps (lyre)	2m 20s
Build mlibc (riscv64, mlibc-static, gcc)	1s
Build mlibc (riscv64, mlibc-shared, gcc)	1s
Compile sysdeps (keyronex)	2m 18s
Compile sysdeps (managarm)	2m 37s
Build mlibc (riscv64, mlibc-ansi-only, gcc)	23s
Build mlibc (riscv64, mlibc-headers-only, gcc)	1s
Compile sysdeps (vinix)	2m 21s
Build mlibc (aarch64, mlibc, gcc)	2m 8s
Compile sysdeps (astral)	2m 19s
Build mlibc (aarch64, mlibc-static, gcc)	26s
Build mlibc (aarch64, mlibc-shared, gcc)	1m 5s
Build mlibc (aarch64, mlibc-ansi-only, gcc)	1m 41s
Build mlibc (aarch64, mlibc-headers-only, gcc)	1m 59s
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)	57s
Build mlibc (m68k, mlibc-static, gcc)	8s
Build mlibc (m68k, mlibc-shared, gcc)	13s
Build mlibc (m68k, mlibc-ansi-only, gcc)	23s
Build mlibc (m68k, mlibc-headers-only, gcc)	26s
Build mlibc (x86_64, mlibc, clang)	1s
	31m 23s

Provide feedback