linker: Make the errors reported by dlopen/dlsym be more useful.

Changed it so that when the linker generates error messages, they are
scribbled away into a buffer that dlfcn and friends can read from.

Since the error messages are generetad with snprintf, and snprintf
MAY call malloc during some code paths, we now link against a version
of libc that does not contain malloc/free/realloc/calloc. We then define
malloc and friends in the dynamic loader, and make them abort() if they
are ever called.

Signed-off-by: Dima Zavin <dima@android.com>

linker/linker.h

@@ -204,6 +204,7 @@ soinfo *find_library(const char *name);
 unsigned unload_library(soinfo *si);
 Elf32_Sym *lookup_in_library(soinfo *si, const char *name);
 Elf32_Sym *lookup(const char *name, unsigned *base);
+const char *linker_get_error(void);
 
 #ifdef ANDROID_ARM_LINKER 
 typedef long unsigned int *_Unwind_Ptr;