Becky/dldt custom build (#4383)

* set NGRAPH_TAG when no TAG file present

* use default build version with custom-build tag
Co-authored-by: Sang Ik Lee <sang.ik.lee@intel.com>

cmake/Modules/git_tags.cmake

@@ -88,9 +88,14 @@ function(NGRAPH_GET_VERSION_LABEL)
                 set(NGRAPH_VERSION_LABEL "v0.0.0+${HASH}" PARENT_SCOPE)
             else()
                 # Not in a git repo
+                if (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/TAG)
+                    # TAG file exists and TAG is assumed to be in the 'correct format', i.e. *.*.*
                     file(READ ${CMAKE_CURRENT_SOURCE_DIR}/TAG NGRAPH_TAG)
                     string(STRIP ${NGRAPH_TAG} NGRAPH_TAG)
                     set(NGRAPH_VERSION_LABEL "${NGRAPH_TAG}" PARENT_SCOPE)
+                else()
+                    set(NGRAPH_VERSION_LABEL "v0.0.0+custom-build" PARENT_SCOPE)
+                endif()
             endif()
         endif()
     endif()