upd: при выполнении make test в каталоге с исходниками не проходит ни одного теста:

=====================================================================
TEST RESULT SUMMARY
---------------------------------------------------------------------
Exts skipped    :    0
Exts tested     :   31
---------------------------------------------------------------------

Number of tests :  330               308
Tests skipped   :   22 (  6.7%) --------
Tests warned    :    0 (  0.0%) (  0.0%)
Tests failed    :  308 ( 93.3%) (100.0%)
Expected fail   :    0 (  0.0%) (  0.0%)
Tests passed    :    0 (  0.0%) (  0.0%)
---------------------------------------------------------------------
Time taken      :   25 seconds
=====================================================================

=====================================================================
FAILED TEST SUMMARY

imagecreatefrompng() and empty/missing file [tests/001.phpt]
Bug #19366 (gdimagefill() function crashes (fixed in bundled libgd)) [tests/bug19366.phpt]
Bug #22544 (TrueColor transparency in PNG images). [tests/bug22544.phpt]
Bug #24155 (gdImageRotate270 rotation problem). [tests/bug24155.phpt]
Bug #24594 (Filling an area using tiles). [tests/bug24594.phpt]
Bug #27582 (ImageFillToBorder() on alphablending image looses alpha on fill color) [tests/bug27582_1.phpt]
Bug #28147 (Crash with anti-aliased line) [tests/bug28147.phpt]
Bug #36697 (TrueColor transparency with GIF palette output). [tests/bug36697.phpt]
Bug #37346 (gdimagecreatefromgif, bad colormap) [tests/bug37346.phpt]
Bug #37360 (gdimagecreatefromgif, bad image sizes) [tests/bug37360.phpt]
Bug #38112 (GIF Invalid Code size ). [tests/bug38112.phpt]
Bug #38179 (imagecopy from a palette to a truecolor image loses alpha channel) [tests/bug38179.phpt]
Bug #38212 (Seg Fault on invalid imagecreatefromgd2part() parameters) [tests/bug38212.phpt]
Bug #39082 (Output image to stdout segfaults). [tests/bug39082.phpt]
Bug #37360 (gdimagecreatefromgif, bad image sizes) [tests/bug39273.phpt]
Bug #39508 (imagefill crashes with small images 3 pixels or less) [tests/bug39286.phpt]
Bug #39366 (imagerotate does not respect alpha with angles>45) [tests/bug39366.phpt]
Bug #39508 (imagefill crashes with small images 3 pixels or less) [tests/bug39508.phpt]
Bug #39780 (PNG image with CRC/data error raises a fatal error) [tests/bug39780.phpt]
Bug #40764 (line thickness not respected for horizontal and vertical lines) [tests/bug40764.phpt]
Bug #41442 (imagegd2() under output control) [tests/bug41442.phpt]
Bug #42434 (ImageLine w/ antialias = 1px shorter) [tests/bug42434.phpt]
Bug #43073 (TrueType bounding box is wrong for angle<>0) [tests/bug43073.phpt]
Bug #43121 (gdImageFill with IMG_COLOR_TILED crashes httpd) [tests/bug43121.phpt]
Bug #43475 (Thick styled lines have scrambled patterns) [tests/bug43475.phpt]
Bug #43828 (broken transparency of imagearc for truecolor in blendingmode) [tests/bug43828.phpt]
Bug #44849 (imagecolorclosesthwb is not available on Windows) [tests/bug44849.phpt]
Bug #45799 (imagepng() crashes on empty image). [tests/bug45799.phpt]
Bug #48555 (ImageFTBBox() differs from previous versions for texts with new lines) [tests/bug48555.phpt]
Bug #48732 (TTF Bounding box wrong for letters below baseline) [tests/bug48732.phpt]
Bug #48801 (Problem with imagettfbbox) [tests/bug48801.phpt]
Bug #49600 (imageTTFText text shifted right) [tests/bug49600.phpt]
Bug #50194 (imagettftext broken on transparent background w/o alphablending) [tests/bug50194.phpt]
Bug #51263 (imagettftext and rotated text uses wrong baseline) [tests/bug51263.phpt]
Bug #51671 (imagefill does not work correctly for small images) [tests/bug51671.phpt]
Bug #53154 (Zero-height rectangle has whiskers) [tests/bug53154.phpt]
Bug #53156 (imagerectangle problem with point ordering) [tests/bug53156.phpt]
Bug #53504 imagettfbbox/imageftbbox gives incorrect values for bounding box [tests/bug53504.phpt]
Bug #53640 (XBM images require width to be multiple of 8) [tests/bug53640.phpt]
Bug #60160 (imagefill does not work correctly for small images) @see bug51671 [tests/bug60160.phpt]
....

> --prefix=/usr/local/php56

нестандартненько

подсказка: а ты рантайм-линкеру (ld.so) об этом как сказал (rpath||ld.so.conf) ?

Тебе же там написало Ask admin to install it.