Missing dependence in Makefile

[O01eg Oleg]

When I try compile ruby with `make -j5` I got such messages:

ruby ./tool/generic_erb.rb --output=id.h \
./template/id.h.tmpl
--vpath=.ext/include/x86_64-linux/ruby:./include/ruby:./enc:./missing
parse.h
id.h updated
gcc -O2 -march=core2 -mtune=core2 -msse -msse2 -msse3 -mmmx -O0 -ggdb3
-fPIC -I. -I.ext/include/x86_64-linux -I./include -I. -DRUBY_EXPORT -o
unicode.o -c ./enc/unicode.c
gcc -O2 -march=core2 -mtune=core2 -msse -msse2 -msse3 -mmmx -O0 -ggdb3
-fPIC -I. -I.ext/include/x86_64-linux -I./include -I. -DRUBY_EXPORT -o
newline.o -c newline.c
Generating RDoc documentation
/miniruby -I./lib -I.ext/common -I./- -r./ext/purelib.rb
/tool/runruby.rb --extout=.ext -- "./bin/rdoc" --no-force-update --all
--ri --op ".ext/rdoc" "."
gcc -O2 -march=core2 -mtune=core2 -msse -msse2 -msse3 -mmmx -O0 -ggdb3
-fPIC -I. -I.ext/include/x86_64-linux -I./include -I. -DRUBY_EXPORT -o
dmyversion.o -c dmyversion.c
gcc -O2 -march=core2 -mtune=core2 -msse -msse2 -msse3 -mmmx -O0 -ggdb3
-fPIC -I. -I.ext/include/x86_64-linux -I./include -I. -DRUBY_EXPORT -o
miniprelude.o -c miniprelude.c
gcc -O2 -march=core2 -mtune=core2 -msse -msse2 -msse3 -mmmx -O0 -ggdb3
-fPIC -I. -I.ext/include/x86_64-linux -I./include -I. -DRUBY_EXPORT -o
class.o -c class.c
/bin/sh: ./miniruby: No such file or directory
make: *** [rdoc] Error 127
make: *** Waiting for unfinished jobs....

When I compile in one thread miniruby compiles and this error doesn't
occure.