Add --enable-debug configure option to enable asserts

asserts are still disabled by default.

Makefile.am

@@ -12,7 +12,6 @@ pixmap_DATA = htop.png
 
 AM_CFLAGS += -pedantic -std=c99 -D_XOPEN_SOURCE_EXTENDED -DSYSCONFDIR=\"$(sysconfdir)\" -I"$(top_srcdir)/$(my_htop_platform)"
 AM_LDFLAGS =
-AM_CPPFLAGS = -DNDEBUG
 
 myhtopsources = AvailableMetersPanel.c CategoriesPanel.c CheckItem.c \
 ClockMeter.c ColorsPanel.c ColumnsPanel.c CPUMeter.c CRT.c DiskIOMeter.c DiskIOMeter.h \

configure.ac

@@ -293,8 +293,14 @@ AM_CFLAGS="\
 
 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])
 
+AC_ARG_ENABLE([debug], [AS_HELP_STRING([--enable-debug], [Enable asserts (default: asserts are disabled)])], [enable_debug="$enableval"], [enable_debug=no])
+AS_IF([test "x$enable_debug" = "xyes"], , [AM_CPPFLAGS="$AM_CPPFLAGS -DNDEBUG"])
+
+AC_SUBST([AM_CPPFLAGS])
+
 # Bail out on errors.
 # ----------------------------------------------------------------------
 if test ! -z "$missing_libraries"; then