[asan] Switch allocator to dynamic base address

This ports a proposed memprof fix (llvm#98510), which has a shadow memory and allocator layout that is similar to ASan. Although we have only observed the failure for memprof on a buildbot [*], it could theoretically happen for ASan.

asan_rtl.cpp calls InitializeShadowMemory() - which dynamically/"randomly" chooses a base address for the shadow mapping - prior to InitializeAllocator(). If we are unlucky, the shadow memory may be mapped in the same region where the allocator wants to be.

This patch fixes the issue by changing the allocator to dynamically choosing a base address, as suggested by Vitaly. For comparison, HWASan already dynamically chooses the base addresses for the shadow mapping and allocator.

[*] https://lab.llvm.org/buildbot/#/builders/66/builds/1361/steps/17/logs/stdio

Author: thurstond

compiler-rt/lib/asan/asan_allocator.h

@@ -214,7 +214,7 @@ const uptr kAllocatorSpace = 0x600000000000ULL;
 const uptr kAllocatorSize  =  0x40000000000ULL;  // 4T.
 typedef DefaultSizeClassMap SizeClassMap;
 #  else
-const uptr kAllocatorSpace = 0x500000000000ULL;
+const uptr kAllocatorSpace = ~(uptr)0;
 const uptr kAllocatorSize = 0x40000000000ULL;  // 4T.
 typedef DefaultSizeClassMap SizeClassMap;
 #  endif