ARROW-3214: [C++] Disable insecure warnings in MinGW build
ARROW-3214: [C++] Disable insecure warnings in MinGW build

It's already disabled in MSVC build.

Author: Kouhei Sutou <kou@clear-code.com>

Closes #2539 from kou/cpp-disable-insecure-warnings-with-mingw and squashes the following commits:

c4c96b3a <Kouhei Sutou> Add endif() expression for easy to read
7ac8a8b2 <Kouhei Sutou>  Disable insecure warnings in MinGW build

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