Document problems on MS-Windows with incompatible regex.h headers.

 PROBLEMS: Mention problems on MS-Windows with incompatible
 regex.h headers.

etc/ChangeLog

+2010-03-27  Eli Zaretskii  <eliz@gnu.org>
+
+	* PROBLEMS: Mention problems on MS-Windows with incompatible
+	regex.h headers.
+
 2010-03-15  Francesc Rocher  <rocher@member.fsf.org>
 
 	* MORE.STUFF: Remove CEDET entry, now distributed as part of

etc/PROBLEMS

@@ -2478,6 +2478,26 @@ these GCC versions.  Note that these versions of GCC, 4.0.3, 4.0.4,
 4.1.1, and 4.1.2, are currently the _only_ versions known to succeed
 in building Emacs (as of v22.1).
 
+*** Building the native MS-Windows port fails due to unresolved externals
+
+The linker error messages look like this:
+
+ oo-spd/i386/ctags.o:ctags.c:(.text+0x156e): undefined reference to `_imp__re_set_syntax'
+ collect2: ld returned 1 exit status
+
+This happens because GCC finds an incompatible header regex.h
+somewhere on the include path, before the version of regex.h supplied
+with Emacs.  One such incompatible version of regex.h is part of the
+GnuWin32 Regex package.
+
+The solution is to remove the incompatible regex.h from the include
+path, when compiling Emacs.  Alternatively, re-run the configure.bat
+script with the "-isystem C:/GnuWin32/include" switch (adapt for your
+system's place where you keep the GnuWin32 include files) -- this will
+cause the compiler to search headers in the directories specified by
+the Emacs Makefile _before_ it looks in the GnuWin32 include
+directories.
+
 *** Building the native MS-Windows port with Cygwin GCC can fail.
 
 Emacs may not build using some Cygwin builds of GCC, such as Cygwin