m4: fix build on Rosetta

Fixes: https://trac.macports.org/ticket/64487

devel/m4/Portfile

@@ -9,7 +9,6 @@ categories      devel
 license         GPL-3+
 installs_libs   no
 maintainers     nomaintainer
-platforms       darwin
 description     GNU macro processor
 
 long_description \
@@ -49,6 +48,13 @@ configure.args  --disable-silent-rules \
                 --with-packager-bug-reports=https://trac.macports.org/wiki/Tickets \
                 ac_cv_libsigsegv=no
 
+# Fix for Rosetta: https://trac.macports.org/ticket/64487
+platform darwin {
+    if {${os.major} == 10 && ${build_arch} eq "ppc"} {
+        configure.args-append --build=powerpc-apple-darwin${os.major}
+    }
+}
+
 post-destroot {
     move ${destroot}${prefix}/share/info/m4.info ${destroot}${prefix}/share/info/gm4.info