linker: Add library load and unload hooks for HWASan.

These hooks notify the HWASan runtime library whenever a library is loaded
or unloaded so that it can update its shadow memory.

Bug: 138159093
Test: walleye_hwasan-userdebug boots with+without https://reviews.llvm.org/D65770
Change-Id: I6caf2a6540ed2c0d94db444e806a3c7ba504cabb
diff --git a/libc/private/bionic_globals.h b/libc/private/bionic_globals.h
index d73079e..ef735ba 100644
--- a/libc/private/bionic_globals.h
+++ b/libc/private/bionic_globals.h
@@ -88,6 +88,10 @@
   TlsModules tls_modules;
   BionicAllocator tls_allocator;
 
+  // Values passed from the HWASan runtime (via libc.so) to the loader.
+  void (*load_hook)(ElfW(Addr) base, const ElfW(Phdr)* phdr, ElfW(Half) phnum) = nullptr;
+  void (*unload_hook)(ElfW(Addr) base, const ElfW(Phdr)* phdr, ElfW(Half) phnum) = nullptr;
+
   // Values passed from the linker to libc.so.
   const char* init_progname = nullptr;
   char** init_environ = nullptr;