bpo-38960: DTrace build fix for FreeBSD. (GH-17451)

DTrace build fix for FreeBSD.

- allowing passing an extra flag as it need to define the arch size.
- casting some probe's arguments.

diff --git a/configure.ac b/configure.ac
index ab8e1b7..fee605e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3500,7 +3500,6 @@
 AC_SUBST(DTRACE_HEADERS)
 AC_SUBST(DTRACE_OBJS)
 DTRACE=
-DFLAGS=
 DTRACE_HEADERS=
 DTRACE_OBJS=
 
@@ -3521,7 +3520,7 @@
         [ac_cv_dtrace_link], [dnl
             ac_cv_dtrace_link=no
             echo 'BEGIN{}' > conftest.d
-            "$DTRACE" -G -s conftest.d -o conftest.o > /dev/null 2>&1 && \
+            "$DTRACE" "$DFLAGS" -G -s conftest.d -o conftest.o > /dev/null 2>&1 && \
                 ac_cv_dtrace_link=yes
       ])
     if test "$ac_cv_dtrace_link" = "yes"; then