pkg/57702: multimedia/libva C++ preprocessor "clang -E" fails sanity check

[davshao%gmail.com@localhost]

>Number:         57702
>Category:       pkg
>Synopsis:       multimedia/libva C++ preprocessor "clang -E" fails sanity check
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Nov 18 04:50:00 +0000 2023
>Originator:     David Shao
>Release:        pkgsrc current
>Organization:
>Environment:
FreeBSD xxxxxx 14.0-RELEASE FreeBSD 14.0-RELEASE #0 releng140-n265380-f9716eee8ab4: Tue Nov 14 03:13:04 PST 2023     xxxxx@xxxxxx:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64
>Description:
Following the commit:

Module Name:    pkgsrc
Committed By:   nia
Date:           Fri Nov 17 08:18:08 UTC 2023

Modified Files:
        pkgsrc/multimedia/libva: Makefile

Log Message:
libva: needs FORCE_C_STD

+# error: 'for' loop initial declarations are only allowed in C99 mode
+FORCE_C_STD=           gnu99

FreeBSD 13 and 14 with base compiler clang fail to build

checking whether clang accepts -g... (cached) yes
checking for clang option to accept ISO C89... (cached) none needed
checking whether clang understands -c and -o together... (cached) yes
checking dependency style of clang... (cached) gcc3
checking whether we are using the GNU C++ compiler... no
checking whether clang++ accepts -g... no
checking dependency style of clang++... none
checking how to run the C++ preprocessor... clang -E
configure: error: in `/usr/pkgsrc/multimedia/libva/work/libva-2.20.0':
configure: error: C++ preprocessor "clang -E" fails sanity check
See `config.log' for more details
*** Error code 1

>How-To-Repeat:

>Fix: