[Darwin] Cleanup code via improved GetMacosAlignedVersion()

Checking the OS version via `GetMacosAlignedVersion()` now works in
simulators [1].  Let's use it to simplify `DyldNeedsEnvVariable()`.

[1] 3fb0de8207

Reviewed By: delcypher

Differential Revision: https://reviews.llvm.org/D81197

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

@@ -879,20 +879,10 @@ bool ReexecDisabled() {
   return false;
 }
 
-extern "C" SANITIZER_WEAK_ATTRIBUTE double dyldVersionNumber;
-static const double kMinDyldVersionWithAutoInterposition = 360.0;
-
-bool DyldNeedsEnvVariable() {
-  // Although sanitizer support was added to LLVM on OS X 10.7+, GCC users
-  // still may want use them on older systems. On older Darwin platforms, dyld
-  // doesn't export dyldVersionNumber symbol and we simply return true.
-  if (!&dyldVersionNumber) return true;
+static bool DyldNeedsEnvVariable() {
   // If running on OS X 10.11+ or iOS 9.0+, dyld will interpose even if
-  // DYLD_INSERT_LIBRARIES is not set. However, checking OS version via
-  // GetMacosAlignedVersion() doesn't work for the simulator. Let's instead
-  // check `dyldVersionNumber`, which is exported by dyld, against a known
-  // version number from the first OS release where this appeared.
-  return dyldVersionNumber < kMinDyldVersionWithAutoInterposition;
+  // DYLD_INSERT_LIBRARIES is not set.
+  return GetMacosAlignedVersion() < MacosVersion(10, 11);
 }
 
 void MaybeReexec() {

compiler-rt/lib/sanitizer_common/sanitizer_mac.h

@@ -44,6 +44,7 @@ struct VersionBase {
     return major > other.major ||
            (major == other.major && minor >= other.minor);
   }
+  bool operator<(const VersionType &other) const { return !(*this >= other); }
 };
 
 struct MacosVersion : VersionBase<MacosVersion> {