Fix more GDB build breakage on mingw32

Fix more GDB build breakage on mingw32

With F23's mingw gcc 5.3.0, I'm seeing:

 i686-w64-mingw32-g++ -x c++ -std=gnu++11 -g3 -O0   -I. -I../../src/gdb -I../../src/gdb/common -I../../src/gdb/config -DLOCALEDIR="\"/usr/local/share/locale\"" -DHAVE_CONFIG_H -I../../src/gdb/../include/opcode -I../../src/gdb/../opcodes/.. -I../../src/gdb/../readline/.. -I../../src/gdb/../zlib -I../bfd -I../../src/gdb/../bfd -I../../src/gdb/../include -I../libdecnumber -I../../src/gdb/../libdecnumber  -I../../src/gdb/gnulib/import -Ibuild-gnulib/import   -I/home/pedro/src/expat/install-win32//include   -Wall -Wpointer-arith -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wempty-body -Wunused-but-set-parameter -Wunused-but-set-variable -Wno-sign-compare -Wno-narrowing -Wno-error=maybe-uninitialized -Wno-format -Werror -c -o windows-nat.o -MT windows-nat.o -MMD -MP -MF ./.deps/windows-nat.o.Tpo ../../src/gdb/windows-nat.c
 ../../src/gdb/windows-nat.c: In function 'void windows_create_inferior(target_ops*, const char*, const string&, char**, int)':
 ../../src/gdb/windows-nat.c:2476:7: error: 'replace' is not a member of 'std'
	std::replace (expanded_infcwd.begin (), expanded_infcwd.end (),
	^

gdb/Changelog:
2017-10-06  Pedro Alves  <palves@redhat.com>

	* windows-nat.c: Include <algorithm>.