use _GNU_SOURCE on Linux to have all useful definitions (pthread_rwlock_t) for example

cmake/abi_check.cmake

@@ -20,7 +20,7 @@
 #
 # We use gcc specific preprocessing command and sed/diff, so it will 
 # only be run  on Unix and only if gcc is used.
-IF(CMAKE_COMPILER_IS_GNUCC AND UNIX)
+IF(CMAKE_COMPILER_IS_GNUCC AND Linux)
   IF(CMAKE_C_COMPILER MATCHES "ccache$")
     SET(COMPILER ${CMAKE_C_COMPILER_ARG1})
     STRING(REGEX REPLACE "^ " "" COMPILER ${COMPILER})

config.h.cmake

@@ -18,6 +18,7 @@
 #cmakedefine DOT_FRM_VERSION @DOT_FRM_VERSION@
 /* Headers we may want to use. */
 #cmakedefine STDC_HEADERS 1
+#cmakedefine _GNU_SOURCE 1
 #cmakedefine HAVE_ALLOCA_H 1
 #cmakedefine HAVE_AIO_H 1
 #cmakedefine HAVE_ARPA_INET_H 1

configure.cmake

@@ -49,6 +49,7 @@ ENDIF()
 IF (CMAKE_SYSTEM_NAME MATCHES "Linux")
   SET(TARGET_OS_LINUX 1)
   SET(HAVE_NPTL 1)
+  SET(_GNU_SOURCE 1)
 ELSEIF(CMAKE_SYSTEM_NAME MATCHES "SunOS")
   SET(TARGET_OS_SOLARIS 1)
 ENDIF()