musl libc build, rather than glibc

We've had reports of a couple of issues building against musl libc.

Issues reported:
  - build procedures utilize cat for Guidebook-creation, and cat
    is deprecated in distros that use musl libc.

  - some of the CRASHREPORT code is using library functions that
    are not available in the musl libc environment. The reported
    functions were backtrace() and backtrace_symbols(), which use
    header file /usr/include/execinfo.h.

So we'll try to accommodate this. Since we don't have a means of
autodetecting the musl libc situation during the build (as of yet), the
builder will have to specify 'make musl=1' on the make command line.

Specifying 'musl=1' on the make command line will:
1. ensure that NOCRASHREPORT gets defined in the C preprocessor.
2. set COLCMD to be '../util/stripbs' instead of 'col -bx'.

Closes #1393

util/.gitignore

@@ -11,6 +11,7 @@ lev_comp
 dlb
 dlb_main
 recover
+stripbs
 tilemap
 tileedit
 tile2x11

util/stripbs.c

@@ -0,0 +1,42 @@
+/* NetHack 3.7  stripbs.c                                         */
+/* Copyright (c) Michael Allison, 2025.                                */
+/* NetHack may be freely redistributed.  See license for details. */
+
+/*
+ * a simple filter to strip character-backspace-character
+ * from stdin and write the results to stdout.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+int main(int argc, char *argv[])
+{
+    int stop = 0, trouble = 0;
+    char buf[2];
+    char *cp = &buf[0], *prev = &buf[1];
+
+    *prev = 0;
+    while (!stop) {
+        if ((fread(buf, 1, 1, stdin)) > 0) {
+            if (*cp == 8) {
+		*prev = 0;
+	    } else {
+		if (*prev)
+                    fputc(*prev, stdout);
+		*prev = *cp;
+	    }
+        } else {
+	    if (errno != EOF)
+                trouble = 1;
+	    if (*prev)
+                fputc(*prev, stdout);
+            stop = 1;
+        }
+    }
+    fflush(stdout);
+    fclose(stdout);
+    return trouble ? EXIT_FAILURE : EXIT_SUCCESS;
+}