Ease CMake and legacy build coexistence

Cliff noticed that the CMake git ident was not being updated when
pulling new changes.  This was because it was getting captured at
configuration time and, even if you pull more changes, the CMake
configuration may not be redone automatically if the build files
weren't also changed.

So, this adds a new target to get the information at build time
instead.

cmake-proxies/cmake-modules/Version.cmake

@@ -0,0 +1,16 @@
+# Executed during build (NOT configuration) to create/update the
+# RevisionIdent.h header.  It will only update it if there was
+# a change in git.
+
+execute_process(
+   COMMAND
+      ${GIT} show -s "--format=#define REV_LONG \"%H\"%n#define REV_TIME \"%cd\"%n%n"
+   OUTPUT_FILE
+      RevisionIdent.h.in
+   OUTPUT_STRIP_TRAILING_WHITESPACE
+   ERROR_QUIET
+   COMMAND_ECHO STDOUT
+)
+
+configure_file( RevisionIdent.h.in RevisionIdent.h COPYONLY )
+