Default to using fork() for vfork() when no arch specific

implementation of vfork is present.

libc/sysdeps/linux/common/Makefile

@@ -25,7 +25,7 @@ CSRC=	waitpid.c getdnnm.c gethstnm.c getcwd.c ptrace.c \
 	cmsg_nxthdr.c longjmp.c open64.c ftruncate64.c mmap64.c \
 	truncate64.c getrlimit64.c setrlimit64.c creat64.c \
 	llseek.c pread_write.c _exit.c sync.c getdirname.c \
-	sendfile64.c xstatconv.c getdents.c getdents64.c
+	sendfile64.c xstatconv.c getdents.c getdents64.c vfork.c
 ifneq ($(strip $(EXCLUDE_BRK)),y)
 CSRC+=sbrk.c
 endif

libc/sysdeps/linux/common/vfork.c

@@ -0,0 +1,8 @@
+/* Trivial implementation for arches that lack vfork */
+#include <unistd.h>
+#include <sys/types.h>
+
+pid_t vfork(void)
+{
+    return fork();
+}