Allow to build without exporting symbols

When statically linking jemalloc, it may be beneficial not to export its
symbols if it makes sense, which allows the compiler and the linker to do
some further optimizations.

INSTALL

@@ -55,6 +55,11 @@ any of the following arguments (not a definitive list) to 'configure':
     jemalloc overlays the default malloc zone, but makes no attempt to actually
     replace the "malloc", "calloc", etc. symbols.
 
+--without-export
+    Don't export public APIs. This can be useful when building jemalloc as a
+    static library, or to avoid exporting public APIs when using the zone
+    allocator on OSX.
+
 --with-private-namespace=<prefix>
     Prefix all library-private APIs with <prefix>.  For shared libraries,
     symbol visibility mechanisms prevent these symbols from being exported, but

configure.ac

@@ -471,6 +471,13 @@ for stem in ${public_syms}; do
   AC_DEFINE_UNQUOTED([${n}], [${m}])
 done
 
+AC_ARG_WITH([export],
+  [AS_HELP_STRING([--without-export], [disable exporting jemalloc public APIs])],
+  [if test "x$with_export" = "xno"; then
+  AC_DEFINE([JEMALLOC_EXPORT],[])]
+fi]
+)
+
 dnl Do not mangle library-private APIs by default.
 AC_ARG_WITH([private_namespace],
   [AS_HELP_STRING([--with-private-namespace=<prefix>], [Prefix to prepend to all library-private APIs])],