tests/t_backtrace breaks the build on port amd64

[Paul Goyette <paul%whooppee.com@localhost>]

With sources from 2013-07-05 at 02:50:04 which includes rev 1.8 of 
src/tests/lib/libexecinfo/t_backtrace.o (the most recent revision)

dependall ===> tests/lib/libexecinfo
#    create  libexecinfo/t_backtrace.d
CC=/test-bed/tools/bin/x86_64--netbsd-gcc /test-bed/tools/bin/nbmkdep -f 
t_backtrace.d  --      --sysroot=/test-bed/dst   
/test-bed/src/tests/lib/libexecinfo/t_backtrace.c
#    create  libexecinfo/.depend
rm -f .depend
CC=/test-bed/tools/bin/x86_64--netbsd-gcc /test-bed/tools/bin/nbmkdep -s .o\ 
.ln -d -f .depend t_backtrace.d
#    create  libexecinfo/Atffile
rm -f .gdbinit
echo "set solib-absolute-prefix /test-bed/dst" > .gdbinit
#   compile  libexecinfo/t_backtrace.o
/test-bed/tools/bin/x86_64--netbsd-gcc -O2 -std=gnu99  -Wall 
-Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wno-sign-compare  
-Wno-traditional  -Wa,--fatal-warnings -Wreturn-type -Wswitch -Wshadow 
-Wcast-qual -Wwrite-strings -Wextra -Wno-unused-parameter -Wno-sign-compare 
-Wsign-compare -Wformat=2   -Wno-format-zero-length  -Werror 
-Wno-missing-noreturn     --sysroot=/test-bed/dst  -c    
/test-bed/src/tests/lib/libexecinfo/t_backtrace.c
cc1: warnings being treated as errors
/test-bed/src/tests/lib/libexecinfo/t_backtrace.c: In function 
'myfunc1.clone.1':
/test-bed/src/tests/lib/libexecinfo/t_backtrace.c:103:1: error: variable 
'ncalls' might be clobbered by 'longjmp' or 'vfork'


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