Add an empty make command for DTrace .d files to stop an implicit

circular dependency in GNU Make which causes .d files to be
overwritten (Bug 61268)

Author: cjbj

acinclude.m4

@@ -2959,8 +2959,12 @@ dnl DTrace objects
   esac
 
 dnl Generate Makefile.objects entries
+dnl The empty $ac_provsrc command stops an implicit circular dependency
+dnl in GNU Make which causes the .d file to be overwritten (Bug 61268)
   cat>>Makefile.objects<<EOF
 
+$abs_srcdir/$ac_provsrc:;
+
 $ac_bdir[$]ac_hdrobj: $abs_srcdir/$ac_provsrc
 	dtrace -h -C -s $ac_srcdir[$]ac_provsrc -o \$[]@ && \$(SED) -ibak 's,PHP_,DTRACE_,g' \$[]@