Added a check for m4 and throw an error if m4 isn't on the path and t…

…he generated file isn't present (as it would be in a point release). In support of #1739

CMakeLists.txt

@@ -1492,20 +1492,27 @@ ENDIF()
 
 MACRO(GEN_m4 filename)
 
- IF(HAVE_M4)
+ # If m4 isn't present, and the generated file doesn't exist,
+ # it cannot be generated and an error should be thrown.
+ IF(NOT HAVE_M4)
+ IF(NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename.c})
+ MESSAGE(FATAL_ERROR "m4 is required to generate ${filename}.c. Please install m4 so that it is on the PATH and try again.")
+ ENDIF()
+ ENDIF(NOT HAVE_M4)
 
- # If m4 is available, remove generated file if it exists.
- IF(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
- FILE(REMOVE ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
- ENDIF()
+ IF(HAVE_M4)
+ # If m4 is available, remove generated file if it exists.
+ IF(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
+ FILE(REMOVE ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
+ ENDIF()
 
- ADD_CUSTOM_COMMAND(
- OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
- COMMAND ${NC_M4}
- ARGS ${M4FLAGS} ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.m4 > ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
- VERBATIM
- )
-ENDIF(HAVE_M4)
+  ADD_CUSTOM_COMMAND(
+  OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
+  COMMAND ${NC_M4}
+  ARGS ${M4FLAGS} ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.m4 > ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
+  VERBATIM
+  )
+ ENDIF(HAVE_M4)
 ENDMACRO(GEN_m4)
 
 # Binary tests, but ones which depend on value of 'TEMP_LARGE' being defined.