GFORTRAN_VERSION for Darwin

[Jason Bacon <jtocino%gmx.com@localhost>]

Anyone averse to updating the GFORTRAN_VERSION on Darwin x86 to 12?

It is currently 12 on aarch64, but defaults to 7 on x86, which is 
ancient and does not even build on my Mac.

I propose the patch below.  Users can always override by setting 
GFORTRAN_VERSION in ${PREFIX}/etc/mk.conf.

--- gfortran.mk 6 Dec 2022 14:29:58 -0000       1.21
+++ gfortran.mk 21 Jan 2023 00:37:15 -0000
@@ -41,7 +41,7 @@
 # in that case.
 POSSIBLE_GFORTRAN_VERSION?=    ${CC_VERSION:S/gcc-//:C/.[0-9].[0-9]$//}

-.if ${MACHINE_PLATFORM:MDarwin-*-aarch64}
+.if ${MACHINE_PLATFORM:MDarwin-*-*}
 GFORTRAN_VERSION?=     12
 .endif