Problem with Libplot

[Michel Boaventura]

Hello,

I'm trying to compile pspp to windows again, but now using gentoo,
instead of windows itself.
I'm having a little problem with libplot on the last stable snapshot
(pspp-stable-20090129).

The configure script doesn't find it, and the log says:

configure:16497: i686-mingw32-gcc -std=gnu99 -o conftest.exe
-I/usr/i686-mingw32/mingw/include/ -I/home/michel/install_dir/include/
-Wdeclaration-after-statement -I/home/michel/install_dir/include
-L/usr/i686-mingw32/mingw/lib/ -L/home/michel/install_dir/lib/
conftest.c -lplot   >&5
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0xa7):
undefined reference to `_png_create_write_struct'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0xcb):
undefined reference to `_png_create_info_struct'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0xe7):
undefined reference to `_png_destroy_write_struct'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x118):
undefined reference to `_png_destroy_write_struct'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x139):
undefined reference to `_png_init_io'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x212):
undefined reference to `_png_set_IHDR'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x383):
undefined reference to `_png_set_tRNS'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x5f6):
undefined reference to `_png_set_text'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x608):
undefined reference to `_png_write_info'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x688):
undefined reference to `_png_set_interlace_handling'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x80b):
undefined reference to `_png_write_rows'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x84c):
undefined reference to `_png_write_end'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x85f):
undefined reference to `_png_destroy_write_struct'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x9a7):
undefined reference to `_png_get_error_ptr'
/home/michel/install_dir/lib//libplot.a(z_write.o):z_write.c:(.text+0x9ee):
undefined reference to `_png_get_error_ptr'
collect2: ld returned 1 exit status

But if I run it myself, passing the argument "-lpng" to gcc, it
compiles without problems. Seems like libplot can't find libpng
without this argument.
Is this a problem of configure script or my enviroment?

Thanks,

Michel