nx-libs breaks with libpng 1.5.x

Archlinux just upgraded libpng 1.4.x to 1.5.8, and it appears to have
broken nx-libs. With libpng 1.4.8, I was able to build nx-libs 3.5.0.9
and successfully run it with x2goserver, but with libpng 1.5.8, when I
try to build nx-libs it gets to compiling Pgn.cpp and fails with
errors:

g++ -c -O3 -fno-rtti -fno-exceptions -I../nx-X11/exports/include
-Wno-deprecated -fPIC -DIN_ADDR_T=in_addr_t -DVERSION=\"3.5.0\"
-DPACKAGE_NAME=\"\" -DPACKAGE_TARNAME=\"\" -DPACKAGE_VERSION=\"\"
-DPACKAGE_STRING=\"\" -DPACKAGE_BUGREPORT=\"\" -Wall -Wpointer-arith
Pgn.cpp

Pgn.cpp: In function ‘int DecompressPng16(unsigned char*, int,
unsigned int, unsigned int, unsigned char*, int)’:
Pgn.cpp:417:15: error: invalid use of incomplete type ‘png_info {aka
struct png_info_def}’
/usr/include/png.h:720:16: error: forward declaration of ‘png_info
{aka struct png_info_def}’

Pgn.cpp: In function ‘int DecompressPng24(unsigned char*, int,
unsigned int, unsigned int, unsigned char*, int)’:
Pgn.cpp:568:15: error: invalid use of incomplete type ‘png_info {aka
struct png_info_def}’
/usr/include/png.h:720:16: error: forward declaration of ‘png_info
{aka struct png_info_def}’

Pgn.cpp: In function ‘int DecompressPng32(unsigned char*, int,
unsigned int, unsigned int, unsigned char*, int)’:
Pgn.cpp:712:15: error: invalid use of incomplete type ‘png_info {aka
struct png_info_def}’