From http://bugzilla.gnome.org/show_bug.cgi?id=370081
Applied upstream in later Mono 1.2 releases.
Index: mono-1.2/support/map.c
===================================================================
--- mono-1.2/support/map.c	(revision 67251)
+++ mono-1.2/support/map.c	(working copy)
@@ -21,7 +21,19 @@
 #define _XOPEN_SOURCE
 #endif /* ndef _XOPEN_SOURCE */
 
+#ifndef L_SET
+#define L_SET SEEK_SET
+#endif /* ndef L_SET */
 
+#ifndef L_INCR
+#define L_INCR SEEK_CUR
+#endif /* ndef L_INCR */
+
+#ifndef L_XTND
+#define L_XTND SEEK_END
+#endif /* ndef L_XTND */
+
+
 /*
  * Implementation Includes
  */
Index: Makefile.am
===================================================================
--- mono-1.2/support/Makefile.am	(revision 67251)
+++ mono-1.2/support/Makefile.am	(working copy)
@@ -114,6 +114,9 @@
 	--impl-header="<dirent.h>"                            \
 	--impl-header="<utime.h>"                             \
 	--impl-header="\"mph.h\""                             \
+	--impl-macro="L_SET=SEEK_SET"                         \
+	--impl-macro="L_INCR=SEEK_CUR"                        \
+	--impl-macro="L_XTND=SEEK_END"                        \
 	--rename-member=st_atime=st_atime_                    \
 	--rename-member=st_ctime=st_ctime_                    \
 	--rename-member=st_mtime=st_mtime_                    \