Remove unused PHP_TARGET_RDYNAMIC m4 macro

This has been once used with apache sapi. Since PHP 7.0 it is not used
in the PHP anymore.

acinclude.m4

@@ -271,25 +271,6 @@ dnl -------------------------------------------------------------------------
 dnl Compiler characteristics checks
 dnl -------------------------------------------------------------------------
 
-dnl
-dnl PHP_TARGET_RDYNAMIC
-dnl
-dnl Checks whether -rdynamic is supported by the compiler.  This
-dnl is necessary for some targets to populate the global symbol
-dnl table.  Otherwise, dynamic modules would not be able to resolve
-dnl PHP-related symbols.
-dnl
-dnl If successful, adds -rdynamic to PHP_LDFLAGS.
-dnl
-AC_DEFUN([PHP_TARGET_RDYNAMIC],[
-  if test -n "$GCC"; then
-    PHP_CHECK_GCC_ARG(-rdynamic, gcc_rdynamic=yes)
-    if test "$gcc_rdynamic" = "yes"; then
-      PHP_LDFLAGS="$PHP_LDFLAGS -rdynamic"
-    fi
-  fi
-])
-
 dnl
 dnl PHP_RUNPATH_SWITCH
 dnl