Axel Huebl ba06eb72d0 libpng: zlib path (#5581) ...

explicitly set the zlib path for libpng configure.

fixes:
```
     [ ... ]
     92    checking for memset... yes
     93    checking for pow... no
     94    checking for pow in -lm... yes
     95    checking for clock_gettime... yes
     96    checking for zlibVersion in -lz... no
     97    checking for z_zlibVersion in -lz... no
  >> 98    configure: error: zlib not installed
```

2017-10-03 14:58:28 -06:00

..

spack

libpng: zlib path (#5581)

2017-10-03 14:58:28 -06:00