Add macro for checking if symbol exists

Modules/CheckSymbolExists.cmake

@@ -0,0 +1,47 @@
+#
+# Check if the symbol exists in include files
+#
+# CHECK_SYMBOL_EXISTS - macro which checks the symbol exists in include files.
+# SYMBOL - symbol
+# FILES  - include files to check
+# VARIABLE - variable to return result
+#
+
+MACRO(CHECK_SYMBOL_EXISTS SYMBOL FILES VARIABLE)
+  IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
+    SET(CHECK_SYMBOL_EXISTS_CONTENT "/* */\n")
+    SET(MACRO_CHECK_SYMBOL_EXISTS_FLAGS ${CMAKE_REQUIRED_FLAGS})
+    STRING(ASCII 35 POUND)
+    STRING(ASCII 40 OPEN_PARENT)
+    STRING(ASCII 41 CLOSE_PARENT)
+    SET(PARENTS "${OPEN_PARENT}${CLOSE_PARENT}")
+    FOREACH(FILE ${FILES})
+      SET(CHECK_SYMBOL_EXISTS_CONTENT
+            "${CHECK_SYMBOL_EXISTS_CONTENT}${POUND}include <${FILE}>\n")
+    ENDFOREACH(FILE)
+    SET(CHECK_SYMBOL_EXISTS_CONTENT
+        "${CHECK_SYMBOL_EXISTS_CONTENT}\n\nvoid main${PARENTS}{"
+        "\n${POUND}ifndef ${SYMBOL}\nchar ${OPEN_PARENT}*f${CLOSE_PARENT} ${PARENTS} = ${SYMBOL};\n${POUND}endif\nreturn 0;\n}\n")
+    WRITE_FILE(${CMAKE_BINARY_DIR}/CMakeTmp/CheckSymbolExists.c 
+               "${CHECK_SYMBOL_EXISTS_CONTENT}")
+    
+    MESSAGE(STATUS "Looking for ${SYMBOL} in ${FILES}")
+    TRY_COMPILE(${VARIABLE}
+               ${CMAKE_BINARY_DIR}
+               ${CMAKE_BINARY_DIR}/CMakeTmp/CheckSymbolExists.c
+               CMAKE_FLAGS 
+                -DCOMPILE_DEFINITIONS:STRING=${MACRO_CHECK_SYMBOL_EXISTS_FLAGS}
+               OUTPUT_VARIABLE OUTPUT)
+    IF(${VARIABLE})
+      MESSAGE(STATUS "Looking for ${SYMBOL} in ${FILES} - found")
+      SET(${VARIABLE} 1 CACHE INTERNAL "Have symbol ${SYMBOL}")
+    ELSE(${VARIABLE})
+      MESSAGE(STATUS "Looking for ${SYMBOL} in ${FILES} - not found.")
+      SET(${VARIABLE} "" CACHE INTERNAL "Have symbol ${SYMBOL}")
+      WRITE_FILE(${CMAKE_BINARY_DIR}/CMakeError.log 
+        "Determining if the ${SYMBOL} "
+        "exist failed with the following output:\n"
+        "${OUTPUT}\n" APPEND)
+    ENDIF(${VARIABLE})
+  ENDIF("${VARIABLE}" MATCHES "^${VARIABLE}$")
+ENDMACRO(CHECK_SYMBOL_EXISTS)