You should enable -g (or higher) for debugging!
>>> Unpacking source...
>>> Unpacking glpng-1.45.tar.bz2 to /var/tmp/portage/media-libs/glpng-1.45-r1/work
>>> Source unpacked in /var/tmp/portage/media-libs/glpng-1.45-r1/work
>>> Compiling source in /var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45 ...
loading initial cache file /var/tmp/portage/media-libs/glpng-1.45-r1/temp/gentoo_common_config.cmake
-- The C compiler identification is GNU
-- Check for working C compiler: /usr/bin/x86_64-pc-linux-gnu-gcc
-- Check for working C compiler: /usr/bin/x86_64-pc-linux-gnu-gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Found ZLIB: /lib64/libz.so
-- Found PNG: /usr/lib64/libpng.so
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so - found
-- Looking for gethostbyname
-- Looking for gethostbyname - found
-- Looking for connect
-- Looking for connect - found
-- Looking for remove
-- Looking for remove - found
-- Looking for shmat
-- Looking for shmat - found
-- Looking for IceConnectionNumber in ICE
-- Looking for IceConnectionNumber in ICE - found
-- Found X11: /usr/lib64/libX11.so
-- Configuring done
-- Generating done
-- Build files have been written to: /var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng_build
make -j2 
Scanning dependencies of target static
Scanning dependencies of target shared
[ 50%] [100%] Building C object src/CMakeFiles/shared.dir/glpng.c.o
Building C object src/CMakeFiles/static.dir/glpng.c.o
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c: In function ‘pngLoadRawF’:
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c:271: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c: In function ‘pngLoadF’:
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c:375: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c: In function ‘pngLoadRawF’:
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c:271: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c: In function ‘pngLoadF’:
/var/tmp/portage/media-libs/glpng-1.45-r1/work/glpng-1.45/src/glpng.c:375: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result
Linking C static library libglpng.a
Linking C shared library libglpng.so
[100%] Built target static
[100%] Built target shared
>>> Source compiled.
>>> Test phase [not enabled]: media-libs/glpng-1.45-r1

>>> Install glpng-1.45-r1 into /var/tmp/portage/media-libs/glpng-1.45-r1/image/ category media-libs
make -j2 install DESTDIR=/var/tmp/portage/media-libs/glpng-1.45-r1/image/ 
[ 50%] Built target shared
[100%] Built target static
Install the project...
-- Install configuration: "Release"
-- Installing: /var/tmp/portage/media-libs/glpng-1.45-r1/image/usr/include/GL/glpng.h
-- Installing: /var/tmp/portage/media-libs/glpng-1.45-r1/image/usr/lib/libglpng.so.1.45
-- Installing: /var/tmp/portage/media-libs/glpng-1.45-r1/image/usr/lib/libglpng.so.1
-- Installing: /var/tmp/portage/media-libs/glpng-1.45-r1/image/usr/lib/libglpng.so
-- Removed runtime path from "/var/tmp/portage/media-libs/glpng-1.45-r1/image//usr/lib/libglpng.so.1.45"
-- Installing: /var/tmp/portage/media-libs/glpng-1.45-r1/image/usr/lib/libglpng.a
>>> Completed installing glpng-1.45-r1 into /var/tmp/portage/media-libs/glpng-1.45-r1/image/

strip: x86_64-pc-linux-gnu-strip --strip-unneeded -R .comment
   usr/lib/libglpng.so.1.45
   usr/lib/libglpng.a
Files matching a file type that is not allowed:
   usr/lib/libglpng.so.1.45
 * 
 * ERROR: media-libs/glpng-1.45-r1 failed.
 * Call stack:
 *       misc-functions.sh, line 717:  Called install_qa_check
 *       misc-functions.sh, line 454:  Called die
 * The specific snippet of code:
 *   		[[ ${abort} == yes ]] && die "multilib-strict check failed!"
 *  The die message:
 *   multilib-strict check failed!
 * 
 * If you need support, post the topmost build error, and the call stack if relevant.
 * A complete build log is located at '/var/tmp/portage/media-libs/glpng-1.45-r1/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/media-libs/glpng-1.45-r1/temp/environment'.
 *