boost-libs on macOS Ventura (13.x)

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

devel/boost-libs fails to build with the error below.  What I've managed
to figure out so far is that "-x c" is incompatible with "-std=c++14" on
recent versions of clang (macOS Ventura aarch64, macOS Monterey x86,
FreeBSD 13).  Odd thing is, I'm not seeing -std=c++14 in the compile
command shown.  Any suggestions would be appreciated...

===

...updating 15 targets...
clang-darwin.compile.c
bin.v2/libs/container/build/clang-darwin-14/release/pch-off/threading-multi/visibility-hidden/alloc_lib.o
error: invalid argument '-std=c++14' not allowed with 'C'

    "clang++" -x c -fPIC -O3 -Wall -fvisibility=hidden -Wno-inline
--target=arm64-apple-darwin  -DBOOST_ALL_NO_LIB=1
-DBOOST_CONTAINER_DYN_LINK=1 -DNDEBUG -I"."  -c -o
"bin.v2/libs/container/build/clang-darwin-14/release/pch-off/threading-multi/visibility-hidden/alloc_lib.o"
"libs/container/src/alloc_lib.c"

...failed clang-darwin.compile.c
bin.v2/libs/container/build/clang-darwin-14/release/pch-off/threading-multi/visibility-hidden/alloc_lib.o...
...skipped
<pbin.v2/libs/container/build/clang-darwin-14/release/pch-off/threading-multi/visibility-hidden>libboost_container.dylib
for lack of
<pbin.v2/libs/container/build/clang-darwin-14/release/pch-off/threading-multi/visibility-hidden>alloc_lib.o...