formula_installer: fix --default-fortran-flags
formula_installer: fix --default-fortran-flags

Setting the `FC` environment variable allows the user to override the
default Fortran compiler. The `SharedEnvExtension#fortran` method then
checks whether any of `FCFLAGS` and `FFLAGS` environment variables are
set and, if not, suggests to use `--default-fortran-flags` when running
`brew install`. However, `--default-fortran-flags` never makes it to
`build.rb` (that is executed by `FormulaInstaller`) because the flag is
not whitelisted in `FormulaInstaller#sanitized_ARGV_options`.

This change rectifies this and thereby eliminates the confusing message.

Fixes #47852.

kevinastone/homebrew,esamson/homebrew,jamer/homebrew,afh/homebrew,muellermartin/homebrew,hanxue/homebrew,base10/homebrew,youtux/homebrew,Chilledheart/homebrew,ablyler/homebrew,skinny-framework/homebrew,chadcatlett/homebrew,base10/homebrew,bukzor/linuxbrew,MartinDelille/homebrew,vigo/homebrew,utzig/homebrew,MoSal/homebrew,redpen-cc/homebrew,MoSal/homebrew,benjaminfrank/homebrew,miketheman/homebrew,galaxy001/homebrew,sometimesfood/homebrew,treyharris/homebrew,benjaminfrank/homebrew,MartinDelille/homebrew,chadcatlett/homebrew,drewwells/homebrew,johanhammar/homebrew,drewwells/homebrew,lrascao/homebrew,MoSal/homebrew,SteveClement/homebrew,dongcarl/homebrew,recruit-tech/homebrew,kodabb/homebrew,yumitsu/homebrew,iandennismiller/homebrew,liamstask/homebrew,gicmo/homebrew,slyphon/homebrew,elyscape/homebrew,knpwrs/homebrew,johanhammar/homebrew,AlexejK/homebrew,DoomHammer/linuxbrew,iandennismiller/homebrew,ento/homebrew,emcrisostomo/homebrew,TaylorMonacelli/homebrew,mobileoverlord/homebrew-1,galaxy001/homebrew,reelsense/linuxbrew,johanhammar/homebrew,polishgeeks/homebrew,SuperNEMO-DBD/cadfaelbrew,scpeters/homebrew,alebcay/homebrew,nandub/homebrew,hakamadare/homebrew,thinker0/homebrew,sakra/homebrew,jsjohnst/homebrew,haihappen/homebrew,scpeters/homebrew,treyharris/homebrew,mactkg/homebrew,mactkg/homebrew,josa42/homebrew,iostat/homebrew2,scorphus/homebrew,LinusU/homebrew,Asuranceturix/homebrew,menivaitsi/homebrew,scorphus/homebrew,apjanke/homebrew,retrography/homebrew,elyscape/homebrew,drbenmorgan/linuxbrew,cscetbon/homebrew,joshfriend/homebrew,youtux/homebrew,ablyler/homebrew,influxdata/homebrew,AlexejK/homebrew,dericed/homebrew,ryanfb/homebrew,kevinastone/homebrew,bukzor/linuxbrew,sjackman/linuxbrew,haihappen/homebrew,skinny-framework/homebrew,dplarson/homebrew,MoSal/homebrew,slyphon/homebrew,emcrisostomo/homebrew,osimola/homebrew,quantumsteve/homebrew,liamstask/homebrew,pdxdan/homebrew,yazuuchi/homebrew,elgertam/homebrew,reelsense/homebrew,decors/homebrew,drewwells/homebrew,emcrisostomo/homebrew,frodeaa/homebrew,frodeaa/homebrew,TaylorMonacelli/homebrew,reelsense/homebrew,Homebrew/linuxbrew,princeofdarkness76/homebrew,3van/homebrew,teslamint/homebrew,adamliter/homebrew,Angeldude/linuxbrew,ento/homebrew,Homebrew/homebrew,eighthave/homebrew,LinusU/homebrew,getgauge/homebrew,jarrettmeyer/homebrew,mkrapp/homebrew,sjackman/linuxbrew,brunchboy/homebrew,theeternalsw0rd/homebrew,Homebrew/homebrew,scorphus/homebrew,skatsuta/homebrew,theeternalsw0rd/homebrew,esamson/homebrew,zchee/homebrew,drbenmorgan/linuxbrew,apjanke/homebrew,dickeyxxx/homebrew,AlexejK/homebrew,ear/homebrew,ybott/homebrew,dalanmiller/homebrew,drewwells/homebrew,ear/homebrew,scorphus/homebrew,ryanfb/homebrew,elyscape/homebrew,ento/homebrew,sferik/homebrew,dericed/homebrew,tschoonj/homebrew,TaylorMonacelli/homebrew,jamer/homebrew,knpwrs/homebrew,utzig/homebrew,zchee/homebrew,ablyler/homebrew,lrascao/homebrew,OJFord/homebrew,deorth/homebrew,drbenmorgan/linuxbrew,menivaitsi/homebrew,youtux/homebrew,liamstask/homebrew,SteveClement/homebrew,pcottle/homebrew,scpeters/homebrew,elyscape/homebrew,gnubila-france/linuxbrew,filcab/homebrew,ilovezfs/homebrew,chadcatlett/homebrew,TaylorMonacelli/homebrew,eighthave/homebrew,menivaitsi/homebrew,royhodgman/homebrew,jamer/homebrew,skinny-framework/homebrew,danieroux/homebrew,base10/homebrew,3van/homebrew,haihappen/homebrew,drbenmorgan/linuxbrew,yazuuchi/homebrew,polishgeeks/homebrew,ralic/homebrew,alebcay/homebrew,mmizutani/homebrew,alebcay/homebrew,theeternalsw0rd/homebrew,quantumsteve/homebrew,SuperNEMO-DBD/cadfaelbrew,retrography/homebrew,influxdb/homebrew,sjackman/linuxbrew,marcwebbie/homebrew,kevinastone/homebrew,reelsense/homebrew,iostat/homebrew2,knpwrs/homebrew,mobileoverlord/homebrew-1,Homebrew/linuxbrew,scpeters/homebrew,dalanmiller/homebrew,pcottle/homebrew,elgertam/homebrew,ExtremeMan/homebrew,dongcarl/homebrew,bukzor/linuxbrew,OJFord/homebrew,teslamint/homebrew,pdxdan/homebrew,gnubila-france/linuxbrew,tutumcloud/homebrew,pdxdan/homebrew,saketkc/linuxbrew,dongcarl/homebrew,sakra/homebrew,marcwebbie/homebrew,youtux/homebrew,cosmo0920/homebrew,benjaminfrank/homebrew,influxdb/homebrew,afh/homebrew,teslamint/homebrew,ebouaziz/linuxbrew,adamliter/homebrew,josa42/homebrew,hakamadare/homebrew,Chilledheart/homebrew,ryanfb/homebrew,Homebrew/homebrew,galaxy001/homebrew,sjackman/linuxbrew,SteveClement/homebrew,mmizutani/homebrew,ilovezfs/homebrew,georgschoelly/homebrew,getgauge/homebrew,hakamadare/homebrew,princeofdarkness76/homebrew,galaxy001/homebrew,MartinDelille/homebrew,sferik/homebrew,treyharris/homebrew,Red54/homebrew,iostat/homebrew2,DoomHammer/linuxbrew,booi/homebrew,keith/homebrew,zchee/homebrew,esamson/homebrew,kodabb/homebrew,influxdata/homebrew,esamson/homebrew,kenips/homebrew,eighthave/homebrew,iandennismiller/homebrew,LinusU/homebrew,redpen-cc/homebrew,3van/homebrew,Homebrew/homebrew,danieroux/homebrew,totalvoidness/homebrew,sometimesfood/homebrew,sometimesfood/homebrew,ExtremeMan/homebrew,benjaminfrank/homebre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