Rename interface for querying physical hardware concurrency

Based on post-commit review for D25585/r284180, rename
hardware_physical_concurrency to heavyweight_hardware_concurrency,
to better reflect what type of tasks it should be used for and
to enable other systems to map this to something other than the
number of physical cores.

llvm-svn: 284390
diff --git a/llvm/unittests/Support/Threading.cpp b/llvm/unittests/Support/Threading.cpp
index 30a3c74..be53026 100644
--- a/llvm/unittests/Support/Threading.cpp
+++ b/llvm/unittests/Support/Threading.cpp
@@ -16,7 +16,7 @@
 namespace {
 
 TEST(Threading, PhysicalConcurrency) {
-  auto Num = hardware_physical_concurrency();
+  auto Num = heavyweight_hardware_concurrency();
   // Since Num is unsigned this will also catch us trying to
   // return -1.
   ASSERT_LE(Num, thread::hardware_concurrency());