Build System & core/heap: add method to disable heap allocator

The heap allocator was found to be hiding a use-after-free error
in an unrelated program (not Atheme IRC Services).

Add a configure option to make mowgli.heap just wrap around
mowgli.alloc directly. This allows hardened memory allocators to
be plugged into the latter, which affect all individual object
allocations made by the former.

The disabled implementation also features more debug logging.

configure

@@ -735,6 +735,7 @@ enable_shared
 enable_static
 with_openssl
 enable_examples
+enable_heap_allocator
 '
       ac_precious_vars='build_alias
 host_alias
@@ -1373,6 +1374,8 @@ Optional Features:
   --disable-shared        do not build shared library
   --enable-static         build static library
   --enable-examples       build examples
+  --disable-heap-allocator
+                          Disable the heap allocator
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -4704,6 +4707,20 @@ fi
 
 
 
+# Check whether --enable-heap-allocator was given.
+if test "${enable_heap_allocator+set}" = set; then :
+  enableval=$enable_heap_allocator; if test x"$enable_heap_allocator" = x"no"; then :
+
+
+$as_echo "#define DISABLE_HEAP_ALLOCATOR 1" >>confdefs.h
+
+fi
+
+else
+  enable_heap_allocator="yes"
+fi
+
+
 
 	# Extract the first word of "tput", so it can be a program name with args.
 set dummy tput; ac_word=$2
@@ -6113,6 +6130,7 @@ cat << _EOF_
 
 Configuration:
    OpenSSL support: ${OPENSSL}
+   Heap allocator: ${enable_heap_allocator}
    Examples: ${EXAMPLES}
 
 Now type "make" to build, and "make install" to install.

configure.ac

@@ -142,6 +142,12 @@ AS_IF([test x"$enable_examples" = x"yes"], [
 
 AC_SUBST(EXAMPLES_BUILD)
 
+AC_ARG_ENABLE([heap-allocator],
+   [AS_HELP_STRING([--disable-heap-allocator], [Disable the heap allocator])],
+   [AS_IF([test x"$enable_heap_allocator" = x"no"], [
+      AC_DEFINE([DISABLE_HEAP_ALLOCATOR], [1], [Disable the heap allocator])])
+   ], [enable_heap_allocator="yes"])
+
 BUILDSYS_INIT
 BUILDSYS_TOUCH_DEPS
 
@@ -152,6 +158,7 @@ cat << _EOF_
 
 Configuration:
    OpenSSL support: ${OPENSSL}
+   Heap allocator: ${enable_heap_allocator}
    Examples: ${EXAMPLES}
 
 Now type "make" to build, and "make install" to install.