Enable NULL pointer checks via compiler if supported

configure.ac

@@ -169,6 +169,23 @@ m4_define([HTOP_CHECK_LIB],
    ], [$4])
 ])
 
+dnl https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
+AC_DEFUN([AX_CHECK_COMPILE_FLAG],
+[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
+  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
+  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
+  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+    [AS_VAR_SET(CACHEVAR,[yes])],
+    [AS_VAR_SET(CACHEVAR,[no])])
+  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
+AS_VAR_IF(CACHEVAR,yes,
+  [m4_default([$2], :)],
+  [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_COMPILE_FLAGS
+
 AC_ARG_ENABLE(unicode, [AS_HELP_STRING([--enable-unicode], [enable Unicode support])], ,enable_unicode="yes")
 if test "x$enable_unicode" = xyes; then
    HTOP_CHECK_SCRIPT([ncursesw6], [addnwstr], [HAVE_LIBNCURSESW], "ncursesw6-config",
@@ -291,6 +308,8 @@ AM_CFLAGS="\
  -Wunused\
  -Wwrite-strings"
 
+AX_CHECK_COMPILE_FLAG([-Wnull-dereference], [AM_CFLAGS="$AM_CFLAGS -Wnull-dereference"], , [-Werror])
+
 AC_ARG_ENABLE([werror], [AS_HELP_STRING([--enable-werror], [Treat warnings as errors (default: warnings are not errors)])], [enable_werror="$enableval"], [enable_werror=no])
 AS_IF([test "x$enable_werror" = "xyes"], [AM_CFLAGS="$AM_CFLAGS -Werror"])
 AC_SUBST([AM_CFLAGS])