Update docs and improve hipcc error message.

Change-Id: I25636d06959d02cc46c8c476d3948e91ff83ea47


[ROCm/hip commit: bff88d0f63]

projects/hip/CONTRIBUTING.md

@@ -124,6 +124,11 @@ Differences or limitations of HIP APIs as compared to CUDA APIs should be clearl
 - ihipLogStatus should only be called from top-level HIP APIs,and should be called to log and return the error code.  The error code 
   is used by the GetLastError and PeekLastError functions - if a HIP API simply returns, then the error will not be logged correctly.
 
+- All HIP environment variables should begin with the keyword HIP_
+    Environment variables should be long enough to describe their purpose but short enough so they can be remembered - perhaps 10-20 characters, with 3-4 parts separated by underscores.
+    To see the list of current environment variables, along with their values, set HIP_PRINT_ENV and run any hip applications on ROCM platform .
+    HIPCC or other tools may support additional environment variables which should follow the above convention.  
+
 
 
 #### Presubmit Testing:

projects/hip/bin/hipcc

@@ -353,7 +353,7 @@ if ($printHipVersion) {
 }
 if ($runCmd) {
     if ($HIP_PLATFORM eq "hcc" and exists($hipConfig{'HCC_VERSION'}) and $HCC_VERSION ne $hipConfig{'HCC_VERSION'}) {
-        print ("HIP ($HIP_PATH) was built using hcc $hipConfig{'HCC_VERSION'}, but you are using hcc $HCC_VERSION. Please rebuild HIP including cmake.\n") && die ();
+        print ("HIP ($HIP_PATH) was built using hcc $hipConfig{'HCC_VERSION'}, but you are using $HCC_HOME/hcc with version $HCC_VERSION from hipcc. Please rebuild HIP including cmake or update HCC_HOME variable.\n") && die ();
     }
     system ("$CMD") and die ();
 }