[hwasan] Add __hwasan_init constructor to runtime lib.

[hctim]

Summary

Found by an Android toolchain upgrade, inherited module constructors
(like init_have_lse_atomics from the builtins) can sneak into the hwasan
runtime. If these inherited constructors call hwasanified libc
functions, then the HWASan runtime isn't setup enough, and the code
crashes.

Mark the initialized as a high-priority initializer to fix this.

[yabinc]

LGTM. I have verified that it solves the problem of booting hwasan Android build.

[pcc]

LGTM

compiler-rt/lib/hwasan/hwasan.cpp

for (const hwasan_global &global : HwasanGlobalsFor(
            /* base */ 0,
            reinterpret_cast<const ElfW(Phdr) *>(
                reinterpret_cast<const char *>(&__ehdr_start) +
                __ehdr_start.e_phoff),
            __ehdr_start.e_phnum))
     InitializeSingleGlobal(global);
 }
 
-void __hwasan_init() {
+__attribute__((constructor(0))) void __hwasan_init() {
   CHECK(!hwasan_init_is_running);
   if (hwasan_inited) return;
   hwasan_init_is_running = 1;
   SanitizerToolName = "HWAddressSanitizer";
 
   InitTlsSize();
 
   CacheBinaryName();