ktbin fails to build on ppc64el with -O3

works with -O2, ok with gcc-4.8 and -O3

[...]
23: #textin FAILED (tests.at:401)
 24: session cleanup notification ok
 25: FormFeed ok
 26: #strlen and CJK/combining chars ok
 27: #substr and CJK/combining chars ok
 28: #postpad and CJK/combining chars ok
 29: #prepad and CJK/combining chars ok
 30: #time ok
 31: "#logtype ttyrec" and ttyrec2ansi ok
 32: #localtime, #gmtime ok
 33: changing session inside compound commands ok
 34: #foreach, #forall ok
 35: #ctoi ok
 36: infinite recursion ok
 37: names for -r ok

## ------------- ##
## Test results. ##
## ------------- ##

ERROR: All 37 tests were run,
1 failed unexpectedly.