Make HCC ignore register keyword

- (previously would emit a warning)
- Also tweak documentation.

Change-Id: I0f4f00f82f8cc53d420112570f2d7675535e6aea


[ROCm/hip commit: 0a74e00ac8]

projects/hip/bin/hipcc

@@ -73,6 +73,7 @@ if ($HIP_PLATFORM eq "hcc") {
 
     $HIPCXXFLAGS .= " -I$HIP_PATH/include/hcc_detail/cuda";
     $HIPCXXFLAGS .= " -I$HSA_PATH/include";
+    $HIPCXXFLAGS .= " -Wno-deprecated-register";
     $HIPLDFLAGS =  "-hc -L$HCC_HOME/lib -Wl,--rpath=$HCC_HOME/lib -lc++ -ldl -lpthread -Wl,--whole-archive -lmcwamp -Wl,--no-whole-archive";
 
     # Suppress linker warnings in case HCC distribution contains OpenCL/SPIR symbols