ports/binutils: Fix compilation when zstd is installed

binutils uses pkg-config to find zstd for the host when building. If our
zstd port is installed, it finds it instead and ends up including our
own sysroot which is incompatible with host's.

unsetting pkg-config related variables fixes this and allows binutils to
build fine even when zstd is installed. We can now make it a dependency.

userspace/libraries/LibC/unistd.cpp

@@ -627,6 +627,7 @@ int getopt(int argc, char* const argv[], const char* optstring)
 }
 
 int chroot(const char* path)
+{
 	return syscall(SYS_CHROOT, path);
 }