build: add configure-time --enable-gcc-warnings option; avoid warnings

* bootstrap.conf (gnulib_modules): Add "warnings" module.
* configure.ac: Add --enable-gcc-warnings, derived from code in bison.
* src/Makefile.am (AM_CFLAGS): Set to $(WARN_CFLAGS) # $(WERROR_CFLAGS)
* lib/Makefile.am (AM_CFLAGS): Change spelling to $(WARN_CFLAGS)
Don't use $(WERROR_CFLAGS), yet.
* src/system.h (usage): Declare.
* src/base64.c (usage): Declare to be global, for consistency.
* src/timeout.c (usage): Likewise.
* src/truncate.c (usage): Likewise.
* src/getlimits.c (usage): Likewise.
* src/pinky.c (ttyname): Declare with prototype, rather than an
empty argument list.
* src/who.c (ttyname): Likewise.
* src/su.c (crypt, getusershell, setusershell, endusershell): Likewise.

9 files changed, 14 insertions, 10 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index a6bc22925..68c5f75f6 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -26,6 +26,8 @@ no_install__progs = \
 build_if_possible__progs = \
   chroot df hostid nice pinky stty su uname uptime users who
 
+AM_CFLAGS = $(WARN_CFLAGS) # $(WERROR_CFLAGS)
+
 EXTRA_PROGRAMS = \
   $(no_install__progs) \
   $(build_if_possible__progs) \
diff --git a/src/base64.c b/src/base64.c
index bfbd9e051..b5c0f71d2 100644
--- a/src/base64.c
+++ b/src/base64.c
@@ -48,7 +48,7 @@ static struct option const long_options[] =
   {NULL, 0, NULL, 0}
 };
 
-static void
+void
 usage (int status)
 {
   if (status != EXIT_SUCCESS)
diff --git a/src/getlimits.c b/src/getlimits.c
index 2b2bbfeea..2fd6e39a8 100644
--- a/src/getlimits.c
+++ b/src/getlimits.c
@@ -55,7 +55,7 @@
 #define UID_T_MIN 0
 #define GID_T_MIN 0
 
-static void
+void
 usage (int status)
 {
   if (status != EXIT_SUCCESS)
diff --git a/src/pinky.c b/src/pinky.c
index 136abc5c2..957592302 100644
--- a/src/pinky.c
+++ b/src/pinky.c
@@ -40,7 +40,7 @@
 # define MAXHOSTNAMELEN 64
 #endif
 
-char *ttyname ();
+char *ttyname (int);
 
 /* If true, display the hours:minutes since each user has touched
    the keyboard, or blank if within the last minute, or days followed
diff --git a/src/su.c b/src/su.c
index f6b61f773..9f99b7871 100644
--- a/src/su.c
+++ b/src/su.c
@@ -118,10 +118,10 @@
 /* The user to become if none is specified.  */
 #define DEFAULT_USER "root"
 
-char *crypt ();
-char *getusershell ();
-void endusershell ();
-void setusershell ();
+char *crypt (char const *key, char const *salt);
+char *getusershell (void);
+void endusershell (void);
+void setusershell (void);
 
 extern char **environ;
 
diff --git a/src/system.h b/src/system.h
index 21182a47f..020f83b48 100644
--- a/src/system.h
+++ b/src/system.h
@@ -655,3 +655,5 @@ bad_cast (char const *s)
 {
   return (char *) s;
 }
+
+void usage (int status);
diff --git a/src/timeout.c b/src/timeout.c
index 8b506f0c9..e8ecf627f 100644
--- a/src/timeout.c
+++ b/src/timeout.c
@@ -122,7 +122,7 @@ cleanup (int sig)
     _exit (128 + sig);
 }
 
-static void
+void
 usage (int status)
 {
   if (status != EXIT_SUCCESS)
diff --git a/src/truncate.c b/src/truncate.c
index 3bc52ca14..c6f12b7a9 100644
--- a/src/truncate.c
+++ b/src/truncate.c
@@ -91,7 +91,7 @@ parse_len (char const *str, off_t *size)
   return -1;
 }
 
-static void
+void
 usage (int status)
 {
   if (status != EXIT_SUCCESS)
diff --git a/src/who.c b/src/who.c
index 3bc680bc0..692b661b3 100644
--- a/src/who.c
+++ b/src/who.c
@@ -95,7 +95,7 @@
 # define UT_ID(U) "??"
 #endif
 
-char *ttyname ();
+char *ttyname (int);
 
 /* If true, attempt to canonicalize hostnames via a DNS lookup. */
 static bool do_lookup;