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 b/configure
index 85120e4..595c129 100755
--- a/configure
+++ b/configure
@@ -11386,7 +11386,6 @@
 
 
 DTRACE=
-DFLAGS=
 DTRACE_HEADERS=
 DTRACE_OBJS=
 
@@ -11452,7 +11451,7 @@
 else
               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
 
 fi