bug#7790: cannot build dev tree on windows with mingw

[Sam Steingold <sds@gnu.org>]

I cannot build emacs dev tree on windows using mingw.
I did:
 ./configure.bat --no-debug --with-gcc --without-xpm \
    --cflags -IC:/gnu/gnuwin32/include --ldflags -LC:/gnu/gnuwin32/lib
make bootstrap
which eventually failed with

gcc -o oo-spd/i386/ctags.exe    -mno-cygwin -LC:/gnu/gnuwin32/lib
oo-spd/i386/ctags.o oo-spd/i386/getopt.o oo-spd/i386/getopt1.o
oo-spd/i386/ntlib.o oo-spd/i386/regex.o   -ladvapi32
oo-spd/i386/ctags.o:ctags.c:(.text+0x19f3): undefined reference to
`__imp__re_set_syntax'
oo-spd/i386/ctags.o:ctags.c:(.text+0x1a19): undefined reference to
`__imp__re_compile_pattern'
oo-spd/i386/ctags.o:ctags.c:(.text+0x1e6b): undefined reference to
`__imp__re_match'
oo-spd/i386/ctags.o:ctags.c:(.text+0x73ec): undefined reference to
`__imp__re_search'
collect2: ld returned 1 exit status
make: *** [oo-spd/i386/ctags.exe] Error 1

note that the missing symbols are found in regex.o without the __imp_ prefix:

$ nm oo-spd/i386/regex.o
00000000 b .bss
00000000 d .data
00000000 r .rdata
00000000 t .text
         U __alloca
         U __imp____mb_cur_max
         U __imp___pctype
         U __isctype
         U _abort
0000061c t _analyse_first
         U _exit
         U _free
0000083c t _group_in_compile_stack
0000080b t _insert_op1
0000088d t _insert_op2
         U _malloc
         U _memcpy
         U _memset
00003d91 t _mutually_exclusive_p
00003cef T _re_compile_fastmap
00005dc9 T _re_compile_pattern
00000020 d _re_error_msgid
000002dd T _re_iswctype
00005a94 T _re_match
00005a46 T _re_match_2
00004029 t _re_match_2_internal
00000000 D _re_max_failures
00005d7f T _re_search
00005acd T _re_search_2
00003d49 T _re_set_registers
000000bd T _re_set_syntax
000000d0 T _re_set_whitespace_regexp
00000010 C _re_syntax_options
00000010 b _re_syntax_table
000000dd T _re_wctype
         U _realloc
00005dff T _regcomp
000060c4 T _regerror
000008cc t _regex_compile
00005f78 T _regexec
0000614d T _regfree
000005be t _skip_one_char
000007f8 t _store_op1
0000086c t _store_op2
         U _strcpy
         U _strncpy
         U _tolower
00000110 b _whitespace_regexp
         U _write
00000000 T _xmalloc
00000054 T _xrealloc
00000000 b done.0

-- 
Sam Steingold <http://sds.podval.org>