You may encounter output similar to this when compiling libaio (a dependency of multipath-tools) if you have enabled Stack Smashing Protection in your CFLAGS:

io_getevents.os:io_getevents.c:(.text+0xe1): more undefined references to `__stack_chk_fail_local' follow
/usr/lib/gcc/i686-pc-linux-gnu/4.4.3/../../../../i686-pc-linux-gnu/bin/ld: libaio.so.1.0.1: hidden symbol `__stack_chk_fail_local' isn't defined
/usr/lib/gcc/i686-pc-linux-gnu/4.4.3/../../../../i686-pc-linux-gnu/bin/ld: final link failed: Nonrepresentable section on output
collect2: ld returned 1 exit status
make[1]: *** [libaio.so.1.0.1] Error 1
make[1]: Leaving directory `/var/tmp/portage/dev-libs/libaio-0.3.107/work/libaio-0.3.107/src'
make: *** [all] Error 2
emake failed
 * ERROR: dev-libs/libaio-0.3.107 failed (compile phase):
 *   emake failed
 * 
 * Call stack:
 *     ebuild.sh, line   56:  Called src_compile
 *   environment, line 2120:  Called _eapi2_src_compile
 *     ebuild.sh, line  665:  Called die
 * The specific snippet of code:
 *              emake || die "emake failed"
 * 
 * If you need support, post the output of 'emerge --info =dev-libs/libaio-0.3.107',
 * the complete build log and the output of 'emerge -pqv =dev-libs/libaio-0.3.107'.
 * The complete build log is located at '/var/tmp/portage/dev-libs/libaio-0.3.107/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/dev-libs/libaio-0.3.107/temp/environment'.
 * S: '/var/tmp/portage/dev-libs/libaio-0.3.107/work/libaio-0.3.107'

>>> Failed to emerge dev-libs/libaio-0.3.107

To remedy, temporarily remove any and all the following from your CFLAGS and recompile:

-fstack-protector -fPIE -fPIC