[NFC][compiler-rt][hwasan] Move shadow bound variables to hwasan.cpp

This way, other platforms can define these values.

Differential Revision: https://reviews.llvm.org/D105744

compiler-rt/lib/hwasan/hwasan.cpp

@@ -50,6 +50,11 @@ bool hwasan_init_is_running;
 
 int hwasan_report_count = 0;
 
+uptr kLowShadowStart;
+uptr kLowShadowEnd;
+uptr kHighShadowStart;
+uptr kHighShadowEnd;
+
 void Flags::SetDefaults() {
 #define HWASAN_FLAG(Type, Name, DefaultValue, Description) Name = DefaultValue;
 #include "hwasan_flags.inc"

compiler-rt/lib/hwasan/hwasan_linux.cpp

@@ -69,10 +69,6 @@ static void ProtectGap(uptr addr, uptr size) {
 
 uptr kLowMemStart;
 uptr kLowMemEnd;
-uptr kLowShadowEnd;
-uptr kLowShadowStart;
-uptr kHighShadowStart;
-uptr kHighShadowEnd;
 uptr kHighMemStart;
 uptr kHighMemEnd;