ARROW-5364: [C++] Use ASCII rather than UTF-8 in BuildUtils.cmake comment
ARROW-5364: [C++] Use ASCII rather than UTF-8 in BuildUtils.cmake comment

Author: Yosuke Shiro <yosuke.shiro615@gmail.com>

Closes #4340 from shiro615/cpp-fix-comments-to-ascii and squashes the following commits:

d9b1420b <Yosuke Shiro>  Fix UTF-8 comments to ASCII in BuildUtils.cmake

kou/arrow,cpcloud/arrow,majetideepak/arrow,renesugar/arrow,renesugar/arrow,apache/arrow,kou/arrow,laurentgo/arrow,wesm/arrow,cpcloud/arrow,majetideepak/arrow,apache/arrow,xhochy/arrow,icexelloss/arrow,wesm/arrow,kou/arrow,laurentgo/arrow,renesugar/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,kou/arrow,kou/arrow,kou/arrow,renesugar/arrow,cpcloud/arrow,laurentgo/arrow,majetideepak/arrow,laurentgo/arrow,cpcloud/arrow,icexelloss/arrow,icexelloss/arrow,kou/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,laurentgo/arrow,xhochy/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,icexelloss/arrow,apache/arrow,laurentgo/arrow,icexelloss/arrow,cpcloud/arrow,renesugar/arrow,laurentgo/arrow,kou/arrow,xhochy/arrow,wesm/arrow,xhochy/arrow,apache/arrow,wesm/arrow,icexelloss/arrow,renesugar/arrow,xhochy/arrow,kou/arrow,wesm/arrow,apache/arrow,majetideepak/arrow,cpcloud/arrow,renesugar/arrow,xhochy/arrow,apache/arrow,wesm/arrow,kou/arrow,xhochy/arrow,xhochy/arrow,xhochy/arrow,renesugar/arrow,cpcloud/arrow,apache/arrow,majetideepak/arrow,cpcloud/arrow,kou/arrow,icexelloss/arrow,wesm/arrow,apache/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,renesugar/arrow,apache/arrow,renesugar/arrow,kou/arrow,majetideepak/arrow,cpcloud/arrow,renesugar/arrow,laurentgo/arrow,xhochy/arrow,majetideepak/arrow,cpcloud/arrow,icexelloss/arrow,icexelloss/arrow,cpcloud/arrow,renesugar/arrow,laurentgo/arrow,majetideepak/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,cpcloud/arrow,renesugar/arrow,majetideepak/arrow,apache/arrow,kou/arrow,majetideepak/arrow,majetideepak/arrow,cpcloud/arrow,majetideepak/arrow,xhochy/arrow,renesugar/arrow,majetideepak/arrow,wesm/arrow,apache/arrow,renesugar/arrow,apache/arrow,xhochy/arrow,wesm/arrow,apache/arrow,wesm/arrow,xhochy/arrow,apache/arrow,majetideepak/arrow,laurentgo/arrow,majetideepak/arrow,wesm/arrow,laurentgo/arrow