mergetools: adjust Beyond Compare config on Mac/Linux

Set the labels of the Linux and Mac versions of Beyond Compare from
Mercurial's builtin variables, same as the Windows version.

Differential Revision: https://phab.mercurial-scm.org/D5255

mercurial/default.d/mergetools.rc

@@ -101,14 +101,14 b' beyondcompare3.priority=-2'
 beyondcompare3.diffargs=/lro /lefttitle=$plabel1 /righttitle=$clabel /solo /expandall $parent $child
 
 ; Linux version of Beyond Compare
-bcompare.args=$local $other $base -mergeoutput=$output -ro -lefttitle=parent1 -centertitle=base -righttitle=parent2 -outputtitle=merged -automerge -reviewconflicts -solo
+bcompare.args=$local $other $base -mergeoutput=$output -ro -lefttitle=$labellocal -centertitle=$labelbase -righttitle=$labelother -outputtitle=merged -automerge -reviewconflicts -solo
 bcompare.gui=True
 bcompare.priority=-1
 bcompare.diffargs=-lro -lefttitle=$plabel1 -righttitle=$clabel -solo -expandall $parent $child
 
 ; OS X version of Beyond Compare
 bcomposx.executable = /Applications/Beyond Compare.app/Contents/MacOS/bcomp
-bcomposx.args=$local $other $base -mergeoutput=$output -ro -lefttitle=parent1 -centertitle=base -righttitle=parent2 -outputtitle=merged -automerge -reviewconflicts -solo
+bcomposx.args=$local $other $base -mergeoutput=$output -ro -lefttitle=$labellocal -centertitle=$labelbase -righttitle=$labelother -outputtitle=merged -automerge -reviewconflicts -solo
 bcomposx.gui=True
 bcomposx.priority=-1
 bcomposx.diffargs=-lro -lefttitle=$plabel1 -righttitle=$clabel -solo -expandall $parent $child