Fixes up to -std=gnu17
Fixes to signal handler, wrong function types, access to opaque
structs, passing char** to function expecting const char* const*
redeclaration of library functions with wrong signatures
https://bugs.gentoo.org/946129
https://bugs.gentoo.org/946361
--- a/scm.c
+++ b/scm.c
@@ -533,7 +533,7 @@
 static void init_sig1(scm_err, signo, handler)
      int scm_err;
      int signo;
-     SIGRETTYPE (*handler)();
+     SIGRETTYPE (*handler)(int);
 {
   int i = scm_err - SIGNAL_BASE;
   ASRTER(i < NUM_SIGNALS, MAKINUM(i), OUTOFRANGE, "init_sig1");
@@ -932,7 +932,6 @@
 extern char **environ;		/* The Linux man page says this
 				   declaration is necessary. */
 char s_getenv[] = "getenv";
-char *getenv();
 SCM scm_getenv(nam)
      SCM nam;
 {
lendwin returns int, it's ignored in the callee of add_final
--- a/crs.c
+++ b/crs.c
@@ -387,5 +387,5 @@
   make_subr(s_mvwin, tc7_subr_3, lmvwin);
   make_subr(s_box, tc7_subr_3, lbox);
   add_feature("curses");
-  add_final(lendwin);
+  add_final((void (*)(void))lendwin);
 }
--- a/scmmain.c
+++ b/scmmain.c
@@ -86,7 +86,8 @@
      const char **argv;
 {
   char *script_arg = 0;		/* location of SCSH style script file or 0. */
-  char *implpath = 0, **nargv;
+  char *implpath = 0;
+  const char  **nargv;
   int nargc, iverbose = 0, buf0stdin;
   SCM retval;
 /* added by Dai Inukai 2001-03-21 */
@@ -115,7 +116,7 @@
    fpspec = fpsetprec(FP_PE); /* IEEE 64 bit FP mantissa*/
 #endif
   execpath = 0;			/* even when dumped */
-  if ((nargv = script_process_argv(argc, argv))) { /* SCSH style scripts */
+  if ((nargv = (const char **)script_process_argv(argc, argv))) { /* SCSH style scripts */
     script_arg = argv[2];	/* Save for scm_find_execpath() call */
     nargc = script_count_argv(nargv);
   }
--- a/crs.c
+++ b/crs.c
@@ -250,7 +250,7 @@
   if (UNBNDP(arg)) arg = cur_outp;
   ASRTER(NIMP(arg) && OPOUTPORTP(arg), arg, ARG1, s_owidth);
   if (NIMP(*loc_stdscr)) {
-    if (WINP(arg)) return MAKINUM(WIN(arg)->_maxx+1);
+    if (WINP(arg)) return MAKINUM(getmaxx(WIN(arg))+1);
     else return MAKINUM(COLS);
   }
   return MAKINUM(80);
@@ -261,7 +261,7 @@
   if (UNBNDP(arg)) arg = cur_outp;
   ASRTER(NIMP(arg) && OPOUTPORTP(arg), arg, ARG1, s_owidth);
   if (NIMP(*loc_stdscr))
-    if (WINP(arg)) return MAKINUM(WIN(arg)->_maxy+1);
+    if (WINP(arg)) return MAKINUM(getmaxy(WIN(arg))+1);
     else return MAKINUM(LINES);
   return MAKINUM(24);
 }
--- a/scm.c
+++ b/scm.c
@@ -154,7 +154,7 @@
 /* PROF_SIGNAL appears below because it is the last signal
    defined in scm.h and in errmsgs in repl.c  */
 static struct {
-  int signo; SIGRETTYPE (*osig)(); SIGRETTYPE (*nsig)();
+  int signo; SIGRETTYPE (*osig)(int); SIGRETTYPE (*nsig)(int);
 } sigdesc[PROF_SIGNAL - SIGNAL_BASE + 1];
 
 #define NUM_SIGNALS (sizeof(sigdesc)/sizeof(sigdesc[0]))
@@ -478,7 +478,7 @@
 #endif
 
 #ifdef SIGPIPE
-static SIGRETTYPE (*oldpipe) ();
+static SIGRETTYPE (*oldpipe) (int);
 #endif
 
 int case_sensitize_symbols = 0;	/* set to 8 to read case-sensitive symbols */
--- a/posix.c
+++ b/posix.c
@@ -191,7 +191,7 @@
   ve[ 0] = makfrom0str(entry->gr_name);
   ve[ 1] = makfrom0str(entry->gr_passwd);
   ve[ 2] = ulong2num((unsigned long)entry->gr_gid);
-  ve[ 3] = makfromstrs(-1, entry->gr_mem);
+  ve[ 3] = makfromstrs(-1, (const char * const *)entry->gr_mem);
   return ans;
 }
 SCM l_setgr(arg)