posix: add package

core/c/libc/stdlib.odin

@@ -40,10 +40,9 @@ when ODIN_OS == .Linux {
 }
 
 
-when ODIN_OS == .Darwin {
+when ODIN_OS == .Darwin || ODIN_OS == .FreeBSD || ODIN_OS == .OpenBSD {
 	RAND_MAX :: 0x7fffffff
 
-	// GLIBC and MUSL only
 	@(private="file")
 	@(default_calling_convention="c")
 	foreign libc {
@@ -55,6 +54,20 @@ when ODIN_OS == .Darwin {
 	}
 }
 
+when ODIN_OS == .NetBSD {
+	RAND_MAX :: 0x7fffffff
+
+	@(private="file")
+	@(default_calling_convention="c")
+	foreign libc {
+		__mb_cur_max: size_t
+	}
+
+	MB_CUR_MAX :: #force_inline proc() -> size_t {
+		return __mb_cur_max
+	}
+}
+
 // C does not declare what these values should be, as an implementation is free
 // to use any two distinct values it wants to indicate success or failure.
 // However, nobody actually does and everyone appears to have agreed upon these
@@ -99,7 +112,7 @@ foreign libc {
 	at_quick_exit :: proc(func: proc "c" ()) -> int ---
 	exit          :: proc(status: int) -> ! ---
 	_Exit         :: proc(status: int) -> ! ---
-	getenv        :: proc(name: cstring) -> [^]char ---
+	getenv        :: proc(name: cstring) -> cstring ---
 	quick_exit    :: proc(status: int) -> ! ---
 	system        :: proc(cmd: cstring) -> int ---
 
@@ -150,4 +163,4 @@ aligned_free :: #force_inline proc "c" (ptr: rawptr) {
 	} else {
 		free(ptr)
 	}
-}
+}