Update unpack_template.h (#14441)
Update unpack_template.h (#14441)

USE_CASE_RANGE is a GNU C feature. This change will activate
USE_CASE_RANGE on any platform when using GNU C and not on any platform
when a different compiler is being used.

closes #14373
pratapvardhan/pandas,amolkahat/pandas,cython-testbed/pandas,louispotok/pandas,rs2/pandas,jmmease/pandas,MJuddBooth/pandas,harisbal/pandas,gfyoung/pandas,cython-testbed/pandas,datapythonista/pandas,gfyoung/pandas,pandas-dev/pandas,linebp/pandas,zfrenchee/pandas,jmmease/pandas,rs2/pandas,cbertinato/pandas,harisbal/pandas,pratapvardhan/pandas,dsm054/pandas,jreback/pandas,jreback/pandas,nmartensen/pandas,nmartensen/pandas,GuessWhoSamFoo/pandas,cbertinato/pandas,Winand/pandas,cython-testbed/pandas,Winand/pandas,GuessWhoSamFoo/pandas,zfrenchee/pandas,GuessWhoSamFoo/pandas,amolkahat/pandas,nmartensen/pandas,gfyoung/pandas,winklerand/pandas,harisbal/pandas,Winand/pandas,toobaz/pandas,jmmease/pandas,toobaz/pandas,Winand/pandas,kdebrab/pandas,amolkahat/pandas,TomAugspurger/pandas,louispotok/pandas,winklerand/pandas,nmartensen/pandas,zfrenchee/pandas,jorisvandenbossche/pandas,Winand/pandas,jreback/pandas,pratapvardhan/pandas,winklerand/pandas,rs2/pandas,Winand/pandas,datapythonista/pandas,GuessWhoSamFoo/pandas,pandas-dev/pandas,kdebrab/pandas,winklerand/pandas,dsm054/pandas,amolkahat/pandas,DGrady/pandas,louispotok/pandas,cbertinato/pandas,louispotok/pandas,harisbal/pandas,nmartensen/pandas,TomAugspurger/pandas,kdebrab/pandas,toobaz/pandas,jmmease/pandas,pandas-dev/pandas,datapythonista/pandas,jmmease/pandas,DGrady/pandas,rs2/pandas,gfyoung/pandas,linebp/pandas,kdebrab/pandas,toobaz/pandas,jmmease/pandas,amolkahat/pandas,TomAugspurger/pandas,datapythonista/pandas,MJuddBooth/pandas,jreback/pandas,linebp/pandas,MJuddBooth/pandas,jorisvandenbossche/pandas,jreback/pandas,dsm054/pandas,winklerand/pandas,nmartensen/pandas,cython-testbed/pandas,harisbal/pandas,jorisvandenbossche/pandas,toobaz/pandas,pratapvardhan/pandas,zfrenchee/pandas,dsm054/pandas,DGrady/pandas,louispotok/pandas,zfrenchee/pandas,linebp/pandas,MJuddBooth/pandas,DGrady/pandas,jorisvandenbossche/pandas,MJuddBooth/pandas,cbertinato/pandas,DGrady/pandas,linebp/pandas,DGrady/pandas,GuessWhoSamFoo/pandas,winklerand/pandas,pandas-dev/pandas,linebp/pandas,TomAugspurger/pandas,kdebrab/pandas,dsm054/pandas,gfyoung/pandas,cython-testbed/pandas,pratapvardhan/pandas,cbertinato/pandas