Enable -Wconversion for thread.cc

This should help prevent bugs due to unexpected implicit integer
conversions.

Some collateral changes were needed as well to limit the number of casts
that had to be introduced.

Bug: 165843530
Test: m test-art-host-gtests
Change-Id: I091122827001ab335c7e140864f67cdf90fcf8b4
diff --git a/runtime/stack_map.cc b/runtime/stack_map.cc
index d813fd5..5cda030 100644
--- a/runtime/stack_map.cc
+++ b/runtime/stack_map.cc
@@ -140,7 +140,7 @@
   return deduped_offset;
 }
 
-StackMap CodeInfo::GetStackMapForNativePcOffset(uint32_t pc, InstructionSet isa) const {
+StackMap CodeInfo::GetStackMapForNativePcOffset(uintptr_t pc, InstructionSet isa) const {
   uint32_t packed_pc = StackMap::PackNativePc(pc, isa);
   // Binary search.  All catch stack maps are stored separately at the end.
   auto it = std::partition_point(