Please describe the problem:
Linking against glib-2.8.0 on OS X fails because of an undefined _environ symbol.

Steps to reproduce:
1. compile glib
2. compile pango or orbit

Actual results:
No errors during #1.

Crash during #2 with:

gcc -dynamiclib  -o .libs/libpango-1.0.0.1000.0.dylib  .libs/break.o 
.libs/ellipsize.o .libs/fonts.o .libs/glyphstring.o .libs/mapping.o
.libs/modules.o .libs/pango-attributes.o .libs/pango-color.o 
.libs/pango-context.o .libs/pango-coverage.o .libs/pango-engine.o 
.libs/pango-fontmap.o .libs/pango-fontset.o .libs/pango-glyph-item.o 
.libs/pango-item.o .libs/pango-layout.o .libs/pango-markup.o 
.libs/pango-renderer.o .libs/pango-script.o .libs/pango-tabs.o 
.libs/pango-utils.o .libs/reorder-items.o .libs/shape.o 
.libs/pango-enum-types.o -all_load  
mini-fribidi/.libs/libmini-fribidi.a  -L/usr/X11R6/lib 
-L/sw/lib /sw/lib/ libgobject-2.0.dylib 
/sw/lib/libgmodule-2.0.dylib /sw/lib/libglib-2.0.dylib 
/sw/lib/libintl.dylib /sw/lib/libiconv.dylib -lm -install_name  
/sw/lib/libpango-1.0.0.dylib -compatibility_version  1001 
-current_version 1001.0
/usr/bin/libtool: internal link edit command failed
ld: warning prebinding disabled because dependent library: /sw/lib/ 
libgobject-2.0.0.dylib is not prebound
ld: warning multiple definitions of symbol _locale_charset
/sw/lib/libiconv.dylib(localcharset.o) definition of _locale_charset
/sw/lib/libintl.dylib(localcharset.o) definition of _locale_charset
ld: Undefined symbols:
_environ
make[4]: *** [libpango-1.0.la] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [all-recursive] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2


Expected results:
No linker error.

Does this happen every time?
Happens every time I try to force all symbols to be resolved (i.e., *not* using
-undefined suppress).

Other information:
OS X doesn't have an environ symbol...I guess it follows the Single Unix
Specification a little closer than other platforms, so when gutils.c says:

/* According to the Single Unix Specification, environ is not in 
 * any system header, although unistd.h often declares it.
 */
extern char **environ;

That wish isn't sufficient to get it declared. In glib-2.6.6, that declaration
was wrapped in #ifndef HAVE_UNSETENV, so there was no problem since OS X does
have unsetenv(). The equivalent for OS X is NSGetEnviron(), so something like:

#ifdef __APPLE__
#define environ (*_NSGetEnviron())
#else
extern char **environ;
#endif

solves the problem for us. Not sure if there's a way to check for this specific
functionality (instead of basing it on the platform). Have a ./configure check
that tries various ways to access the env, crash if none work?