A special linker for ASan executables.

Setup a /system/bin/linker_asan as a symlink to "linker".
Read the linker name from PT_INTERP, and if it is linker_asan,
switch default library lookup paths to the ASan set, which
starts with the path to the instrumented libraries
(/data/lib), followed by /system/lib as a fallback.

This ensures that ASan binaries prefer ASan libraries, when
available. This approach is way better then RPATH/RUNPATH and even
better than LD_LIBRARY_PATH:
- RUNPATH is per-DSO, while default paths are global.
- LD_LIBRARY_PATH is overwritten by android_update_LD_LIBRARY_PATH.
- neither RUNPATH nor LD_LIBRARY_PATH appear in
  android_get_LD_LIBRARY_PATH which is used to build java.lang.path.
  Having ASan libraries in java.lang.path is a good thing.

Bug: 22355945
Change-Id: I1d2791fbf5740618f18f71a3ae3d873714669d3f

linker/linker_phdr.h

@@ -109,4 +109,7 @@ void phdr_table_get_dynamic_section(const ElfW(Phdr)* phdr_table, size_t phdr_co
                                     ElfW(Addr) load_bias, ElfW(Dyn)** dynamic,
                                     ElfW(Word)* dynamic_flags);
 
+const char* phdr_table_get_interpreter_name(const ElfW(Phdr) * phdr_table, size_t phdr_count,
+                                            ElfW(Addr) load_bias);
+
 #endif /* LINKER_PHDR_H */