[SampleFDO] Enable FSAFDO loading passes if --enable-fs-discriminator is enabled

[xur]

Summary

FSAFDO profile loader is currently disabled even --enable-fs-discriminator is enabled.
They need to be turned on by options which makes it cumbersome for experiments.

This patch changes the FSAFDO profile loader enabled by default. Since they are
guarded by EnableFSDiscriminator, they will only be turned on if
--enable-fs-discriminator is enabled. Note that --enable-fs-discriminator is
still disabled by default.

[hoy]

LGTM.

llvm/lib/CodeGen/TargetPassConfig.cpp

 // This is mainly for debugging and tuning purpose.
 static cl::opt<bool>
     FSNoFinalDiscrim("fs-no-final-discrim", cl::init(false), cl::Hidden,
                      cl::desc("Do not insert FS-AFDO discriminators before "
                               "emit."));
 // Disable MIRProfileLoader before RegAlloc. This is for for debugging and
 // tuning purpose.
 static cl::opt<bool> DisableRAFSProfileLoader(
-    "disable-ra-fsprofile-loader", cl::init(true), cl::Hidden,
+    "disable-ra-fsprofile-loader", cl::init(false), cl::Hidden,
     cl::desc("Disable MIRProfileLoader before RegAlloc"));
 // Disable MIRProfileLoader before BloackPlacement. This is for for debugging
 // and tuning purpose.
 static cl::opt<bool> DisableLayoutFSProfileLoader(
-    "disable-layout-fsprofile-loader", cl::init(true), cl::Hidden,
+    "disable-layout-fsprofile-loader", cl::init(false), cl::Hidden,
     cl::desc("Disable MIRProfileLoader before BlockPlacement"));
 // Specify FSProfile file name.
 static cl::opt<std::string>
     FSProfileFile("fs-profile-file", cl::init(""), cl::value_desc("filename"),
                   cl::desc("Flow Sensitive profile file name."), cl::Hidden);
 // Specify Remapping file for FSProfile.
 static cl::opt<std::string> FSRemappingFile(
     "fs-remapping-file", cl::init(""), cl::value_desc("filename"),