Prefer documented autoconf macro 'm4_if' over 'ifelse'. * m4/autobuild.m4 (AB_INIT): Use m4_if instead of ifelse. * m4/csharpexec.m4 (gt_CSHARPEXEC): Likewise. * m4/javacomp.m4 (gt_JAVACOMP): Likewise. * m4/javaexec.m4 (gt_JAVAEXEC): Likewise. * m4/libtextstyle.m4 (gl_LIBTEXTSTYLE): Likewise.