[calamares] Try to reduce compile-churn with version header

- Very rarely do we need the full-git-version of Calamares,
  so split that into a separate header with a little trickery.
- In the "normal" version header, drop the full-git-version values.

CMakeLists.txt

@@ -537,7 +537,11 @@ if( CALAMARES_VERSION_RC )
     set( CALAMARES_VERSION ${CALAMARES_VERSION}rc${CALAMARES_VERSION_RC} )
 endif()
 
-# additional info for non-release builds
+# Additional info for non-release builds. The "extended" version information
+# with date and git information (commit, dirty status) is used only
+# by CalamaresVersionX.h, which is included by consumers that need a full
+# version number with all that information; normal consumers can include
+# CalamaresVersion.h with more stable numbers.
 if( NOT BUILD_RELEASE AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/.git/" )
     include( CMakeDateStamp )
     set( CALAMARES_VERSION_DATE "${CMAKE_DATESTAMP_YEAR}${CMAKE_DATESTAMP_MONTH}${CMAKE_DATESTAMP_DAY}" )

src/calamares/CalamaresVersion.h.in

@@ -4,7 +4,7 @@
 #cmakedefine CALAMARES_ORGANIZATION_NAME "${CALAMARES_ORGANIZATION_NAME}"
 #cmakedefine CALAMARES_ORGANIZATION_DOMAIN "${CALAMARES_ORGANIZATION_DOMAIN}"
 #cmakedefine CALAMARES_APPLICATION_NAME "${CALAMARES_APPLICATION_NAME}"
-#cmakedefine CALAMARES_VERSION "${CALAMARES_VERSION}"
+#cmakedefine CALAMARES_VERSION "${CALAMARES_VERSION_SHORT}"
 #cmakedefine CALAMARES_VERSION_SHORT "${CALAMARES_VERSION_SHORT}"
 
 #cmakedefine CALAMARES_VERSION_MAJOR "${CALAMARES_VERSION_MAJOR}"

src/calamares/CalamaresVersionX.h.in

@@ -0,0 +1,13 @@
+// Same as CalamaresVersion.h, but with a full-git-extended VERSION
+// rather than the short (vM.m.p) semantic version.
+#ifndef CALAMARES_VERSION_H
+
+// On purpose, do not define the guard, but let CalamaresVersion.h do it
+// #define CALAMARES_VERSION_H
+
+#include "CalamaresVersion.h"
+
+#undef CALAMARES_VERSION
+#cmakedefine CALAMARES_VERSION "${CALAMARES_VERSION}"
+
+#endif  // CALAMARES_VERSION_H