Add stpcpy to autoconf machinery

* configure.ac: Add stpcpy to AC_CHECK_FUNCS.
* defs.h: Frame stpcpy with "if !defined HAVE_STPCPY".
* util.c: Likewise.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/configure.ac b/configure.ac
index 0a4f891..789a997 100644
--- a/configure.ac
+++ b/configure.ac
@@ -235,6 +235,7 @@
 	strsignal \
 	sys_siglist \
 	_sys_siglist \
+	stpcpy \
 ])
 AC_CHECK_HEADERS([ \
 	inttypes.h \
diff --git a/defs.h b/defs.h
index 59d4c7a..dd8fc64 100644
--- a/defs.h
+++ b/defs.h
@@ -681,12 +681,14 @@
 extern void tv_mul(struct timeval *, struct timeval *, int);
 extern void tv_div(struct timeval *, struct timeval *, int);
 
+#if !defined HAVE_STPCPY
 /* Some libc have stpcpy, some don't. Sigh...
  * Roll our private implementation...
  */
 #undef stpcpy
 #define stpcpy strace_stpcpy
 extern char *stpcpy(char *dst, const char *src);
+#endif
 
 #ifdef SUNOS4
 extern int fixvfork(struct tcb *);
diff --git a/util.c b/util.c
index 0277deb..7d1af70 100644
--- a/util.c
+++ b/util.c
@@ -164,6 +164,7 @@
 	return NULL;
 }
 
+#if !defined HAVE_STPCPY
 char *
 stpcpy(char *dst, const char *src)
 {
@@ -171,6 +172,7 @@
 		dst++;
 	return dst;
 }
+#endif
 
 /*
  * Generic ptrace wrapper which tracks ESRCH errors