우분투 20.04 m4 patch

아래와 같은 m4 빌드 에러는 우분투 18.04 이상 버전을 사용할 경우 발생한다. | ../../m4-1.4.17/lib/freadahead.c: In function ‘freadahead’: | ../../m4-1.4.17/lib/freadahead.c:91:3: error: #error "Please port gnulib freadahead.c to your platform! Look at the definition of fflush, fread, ungetc on your system, then report this to bug-gnulib." | 91 | #error "Please port gnulib freadahead.c to your platform! Look at the definitio..