Remove leading zeros in version_config.hpp (#793)

Since we switched to CalVer, the version strings contain leading zeros, e.g. `21.08.00`. This leads to the generated header `version_config.hpp` to contain
```cpp
#define RMM_VERSION_MAJOR 21
#define RMM_VERSION_MINOR 08
#define RMM_VERSION_PATCH 00
```
in which `08` is an invalid octal literal. See the resulting CI failure at https://gpuci.gpuopenanalytics.com/job/rapidsai/job/conda/job/xgboost/job/xgboost-conda-build/229/CUDA=11.0,PYTHON=3.7/console. The generated header is used by XGBoost.

Fix: Remove the leading zeros in the C++ constants so that we'd get
```cpp
```cpp
#define RMM_VERSION_MAJOR 21
#define RMM_VERSION_MINOR 8
#define RMM_VERSION_PATCH 0
```

Authors:
  - Philip Hyunsu Cho (https://github.com/hcho3)

Approvers:
  - Jake Hemstad (https://github.com/jrhemstad)

URL: #793

cmake/Modules/Version.cmake

@@ -13,6 +13,9 @@
 # Generate version_config.hpp from the version found in CMakeLists.txt
 function(write_version)
   message(STATUS "RMM VERSION: ${RMM_VERSION}")
+  math(EXPR RMM_VERSION_MAJOR_CPP_HEADER "${RMM_VERSION_MAJOR} + 0" OUTPUT_FORMAT DECIMAL)
+  math(EXPR RMM_VERSION_MINOR_CPP_HEADER "${RMM_VERSION_MINOR} + 0" OUTPUT_FORMAT DECIMAL)
+  math(EXPR RMM_VERSION_PATCH_CPP_HEADER "${RMM_VERSION_PATCH} + 0" OUTPUT_FORMAT DECIMAL)
   configure_file(${RMM_SOURCE_DIR}/cmake/version_config.hpp.in
                  ${RMM_BINARY_DIR}/include/rmm/version_config.hpp @ONLY)
 endfunction(write_version)

cmake/version_config.hpp.in

@@ -15,6 +15,6 @@
  */
 #pragma once
 
-#define RMM_VERSION_MAJOR @RMM_VERSION_MAJOR@
-#define RMM_VERSION_MINOR @RMM_VERSION_MINOR@
-#define RMM_VERSION_PATCH @RMM_VERSION_PATCH@
+#define RMM_VERSION_MAJOR @RMM_VERSION_MAJOR_CPP_HEADER@
+#define RMM_VERSION_MINOR @RMM_VERSION_MINOR_CPP_HEADER@
+#define RMM_VERSION_PATCH @RMM_VERSION_PATCH_CPP_HEADER@