php 7.4/git build of ext/sodium fails at configure 'syntax error' ?

[PGNet Dev <pgnet.dev@xxxxxxxxx>]

i'm building a clean-install of latest 7.4 branch

	git log | head
		commit d3112adf7f22a6eede0c90218ffd1badcaaad1a0
		Merge: 152ccfb08d 579562176b
		Author: Derick Rethans <github@xxxxxxxxxxxxxxxx>
		Date:   Fri Jun 21 16:52:15 2019 +0100

		    Merge branch 'bug67348-mysqli-stat' into PHP-7.4

		commit 579562176b71820ad49d43b2c841642fef12fe57
		Author: Derick Rethans <github@xxxxxxxxxxxxxxxx>
		Date:   Fri Jun 21 16:50:40 2019 +0100

it's mostly good, but build of ext/sodium fails.

checking in detail,

	rpm -qa | grep libsodium
		libsodium-devel-1.0.17-lp151.74.1.x86_64
		libsodium23-1.0.17-lp151.74.1.x86_64
	pkg-config --modversion libsodium
		1.0.17
	pkg-config --libs libsodium
		-lsodium

	cd ext/sodium/
	phpize
	./configure \
	 --with-sodium \
	 --prefix=/usr/local/test-sodium-ext \
	 --with-php-config=/usr/bin/php-config \
	 --with-gnu-ld

		...
		checking for sodium support... yes, shared
			./configure: line 3906: syntax error near unexpected token `LIBSODIUM,'
			./configure: line 3906: `  PKG_CHECK_MODULES(LIBSODIUM, libsodium >= 1.0.8)'
		...

where

	cat ./configure
			...
				if test "$PHP_SODIUM" != "no"; then
	3906		  PKG_CHECK_MODULES(LIBSODIUM, libsodium >= 1.0.8)
	

*Looks* ok to me at 1st glance.  Why the "syntax error"?

Unclear what's the problem here ...