948105b7a34ec9a9e5479d376b7c86bafee50a01 introduces a test in configure.ac to find pkg-config as a path. but, some time before, 6053cb4f3873897acf5d899bc6f02046d0748a0f normalized the use of pkg-config in the pinentry build process.
the efl pinentry autoconf stanzas ought to use PKG_CHECK_MODULES the same way that gnome3 and gtk2 tests do, rather than overriding the variable for $PKG_CONFIG, which could cause other breakage, especially when cross-building.
for more information, see also debian bug #884798 and [lintian's autotools-pkg-config-macro-not-cross-compilation-safe tag](https://lintian.debian.org/tags/autotools-pkg-config-macro-not-cross-compilation-safe.html).
This was introduced between pinentry 1.1.0 and 1.1.1.