cmake support: first cut from David Vaz work.i

cmake/TestSTDC.cmake

@@ -0,0 +1,36 @@
+# AC_HEADER_STDC is gross overkill since the current PLplot code only uses
+# this for whether or not atexit can be used.  But implement the full suite
+# of AC_HEADER_STDC checks to keep the cmake version in synch with autotools
+# and just in case some PLplot developer assumes the complete check for
+# standard headers is done for a future programming change.
+#
+# From info autoconf....
+# Define STDC_HEADERS if the system has ANSI C header files.
+# Specifically, this macro checks for stdlib.h', stdarg.h',
+# string.h', and float.h'; if the system has those, it probably
+# has the rest of the ANSI C header files.  This macro also checks
+# whether string.h' declares memchr' (and thus presumably the
+# other mem' functions), whether stdlib.h' declare free' (and
+# thus presumably malloc' and other related functions), and whether
+# the ctype.h' macros work on characters with the high bit set, as
+# ANSI C requires.
+
+message(STATUS "Checking whether system has ANSI C header files")
+check_include_files("stdlib.h;stdarg.h;string.h;float.h" StandardHeadersExist)
+if(StandardHeadersExist)
+  check_prototype_exists(memchr string.h memchrExists)
+  if(memchrExists)
+    check_prototype_exists(free stdlib.h freeExists)
+    if(freeExists)
+      include(TestForHighBitCharacters)
+      if(CMAKE_HIGH_BIT_CHARACTERS)
+        message(STATUS "ANSI C header files - found")
+        set(STDC_HEADERS 1 CACHE INTERNAL "System has ANSI C header files")
+      endif(CMAKE_HIGH_BIT_CHARACTERS)
+    endif(freeExists)
+  endif(memchrExists)
+endif(StandardHeadersExist)
+if(NOT STDC_HEADERS)
+  message(STATUS "ANSI C header files - not found")
+  set(STDC_HEADERS 0 CACHE INTERNAL "System has ANSI C header files")
+endif(NOT STDC_HEADERS)