cmake: Check if C macros are correctly parse when building module info (#3191)

The macro **THIS_MODULE_KEYS** could be empty, but the other 4 macros must be non-empty:

- THIS_MODULE_CLASSIC_NAME
- THIS_MODULE_MODERN_NAME
- THIS_MODULE_LIB
- THIS_MODULE_PURPOSE

If any of the 4 macros are not given, given an empty string, or incorrectly parsed by our regex,
the CMake script will report warnings like:

```
CMake Warning at /Users/seisman/Gits/gmt/gmt/cmake/modules/GmtGenExtraHeaders.cmake:111 (message):
  THIS_MODULE_PURPOSE is empty in seis/pssac.c
Call Stack (most recent call first):
  /Users/seisman/Gits/gmt/gmt/cmake/modules/GmtGenExtraHeaders.cmake:130 (gen_gmt_moduleinfo_h)
```

Address #3180.

Author: seisman

cmake/modules/GmtGenExtraHeaders.cmake

@@ -86,16 +86,34 @@ macro (gen_gmt_moduleinfo_h output_header_file)
 	set (_moduleinfo)
 	foreach (_prog_src ${ARGN})
 		file (READ ${GMT_SRC}/src/${_prog_src} _src_content)
+
 		string (REGEX MATCH "#define[ \t]*THIS_MODULE_CLASSIC_NAME[ \t]*\"([^\n]*)\"[ \t]*\n" _this_module_classic_name ${_src_content})
 		set (_this_module_classic_name ${CMAKE_MATCH_1})
+		if ("${_this_module_classic_name}" STREQUAL "")
+			message (WARNING "THIS_MODULE_CLASSIC_NAME is empty in ${_prog_src}")
+		endif ("${_this_module_classic_name}" STREQUAL "")
+
 		string (REGEX MATCH "#define[ \t]*THIS_MODULE_MODERN_NAME[ \t]*\"([^\n]*)\"[ \t]*\n" _this_module_modern_name ${_src_content})
 		set (_this_module_modern_name ${CMAKE_MATCH_1})
+		if ("${_this_module_modern_name}" STREQUAL "")
+			message (WARNING "THIS_MODULE_MODERN_NAME is empty in ${_prog_src}")
+		endif ("${_this_module_modern_name}" STREQUAL "")
+
 		string (REGEX MATCH "#define[ \t]*THIS_MODULE_LIB[ \t]*\"([^\n]*)\"[ \t]*\n" _this_module_lib ${_src_content})
 		set (_this_module_lib ${CMAKE_MATCH_1})
+		if ("${_this_module_lib}" STREQUAL "")
+			message (WARNING "THIS_MODULE_LIB is empty in ${_prog_src}")
+		endif ("${_this_module_lib}" STREQUAL "")
+
 		string (REGEX MATCH "#define[ \t]*THIS_MODULE_PURPOSE[ \t]*\"([^\n]*)\"[ \t]*\n" _this_module_purpose ${_src_content})
 		set (_this_module_purpose ${CMAKE_MATCH_1})
+		if ("${_this_module_purpose}" STREQUAL "")
+			message (WARNING "THIS_MODULE_PURPOSE is empty in ${_prog_src}")
+		endif ("${_this_module_purpose}" STREQUAL "")
+
 		string (REGEX MATCH "#define[ \t]*THIS_MODULE_KEYS[ \t]*\"([^\n]*)\"[ \t]*\n" _this_module_keys ${_src_content})
 		set (_this_module_keys ${CMAKE_MATCH_1})
+
 		list (APPEND _moduleinfo "\t{\"${_this_module_modern_name}\", \"${_this_module_classic_name}\", \"${_this_module_lib}\", \"${_this_module_purpose}\", \"${_this_module_keys}\"},")
 	endforeach (_prog_src ${ARGN})
 	list (JOIN _moduleinfo "\n" _moduleinfo)