user: compile path.c only once

Also merge bsd-user/path.c and linux-user/path.c.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/qemu-common.h b/qemu-common.h
index c1fb5bf..74ac88f 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -115,6 +115,10 @@
 time_t mktimegm(struct tm *tm);
 int qemu_fls(int i);
 
+/* path.c */
+void init_paths(const char *prefix);
+const char *path(const char *pathname);
+
 #define qemu_isalnum(c)		isalnum((unsigned char)(c))
 #define qemu_isalpha(c)		isalpha((unsigned char)(c))
 #define qemu_iscntrl(c)		iscntrl((unsigned char)(c))