use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

src/misc/realpath.c

@@ -6,7 +6,7 @@
 #include <errno.h>
 #include <unistd.h>
 
-char *realpath(const char *filename, char *resolved)
+char *realpath(const char *restrict filename, char *restrict resolved)
 {
 	int fd;
 	ssize_t r;