Switch hwasan from fork to vfork.

Remove the special case for "hwaddress" sanitizer (HWASan) that makes it
use fork instead of vfork (which is the default). The case was
introduced earlier because of the missing support for vfork in HWASan.

HWASan has been fixed more than 2 years ago in
https://reviews.llvm.org/D58533. Moreover, a bug in the fork support has
been discovered and fixed upstream in https://reviews.llvm.org/D108063,
but it is not in the current Android toolchain yet.

Switching back to vfork makes the code faster, avoids the hwasan bug,
and reduces the diff in behavior between hwasan and regular builds.

Bug: 196623668
Test: CtsLibcoreTestCases (no new failures)
Test: manual
Merged-In: I15d32829806f605d5599d776753bc32df0494661
Change-Id: I15d32829806f605d5599d776753bc32df0494661
(cherry picked from commit c88ebe712180722b17c17175f0aa90a002eec8f6)
(cherry picked from commit 023b3e8f102d15f3f421f14a9b317483264be574)
diff --git a/ojluni/src/main/native/UNIXProcess_md.c b/ojluni/src/main/native/UNIXProcess_md.c
index 40fdc18..a3790e8 100644
--- a/ojluni/src/main/native/UNIXProcess_md.c
+++ b/ojluni/src/main/native/UNIXProcess_md.c
@@ -119,8 +119,7 @@
 // Android-changed: disable vfork under AddressSanitizer.
 //  #ifdef __linux__
-  #if defined(__linux__) && !__has_feature(address_sanitizer) && \
-      !__has_feature(hwaddress_sanitizer)
+  #if defined(__linux__) && !__has_feature(address_sanitizer)
     #define START_CHILD_USE_VFORK 1
     #define START_CHILD_USE_VFORK 0