[cairo] PKG_CONFIG undefined during checking for 'cairo's PNG backend', whilst 'checking for pkg-config' looks good.

[Leon Woestenberg]

Hello all,

I am bringing cairo 1.2.6 as an OpenEmbedded package build, but I run
into an undefined PKG_CONFIG variable during configure testing the
availability of png libraries using "--exists", while configure *did*
find the full pkg-config.

I am lost as where the PKG_CONFIG is set or cleared, can someone look
along please?

The two dashes are from an echo "-- $PKG_CONFIG" I introduced.

---<snippet one>---
...
checking for armeb-linux-pkg-config... no
checking for pkg-config...
/home/leon/sandbox/ixp4xx/openembedded/build/tmp/staging/x86_64-linux/bin/pkg-config
checking pkg-config is at least version 0.19... no
checking for X... disabled
checking for cairo's Xlib Xrender backend...
checking whether cairo's Xlib Xrender backend could be enabled... no
(requires --enable-xlib)
checking for cairo's Microsoft Windows font backend...
checking whether cairo's Microsoft Windows font backend could be
enabled... no (disabled, use --enable-win32 to enable)
checking for cairo's PNG backend...
--
/home/leon/sandbox/ixp4xx/openembedded/build/tmp/work/cairo-1.2.6-r0/cairo-1.2.6/configure:
line 25429: --exists: command not found
--
/home/leon/sandbox/ixp4xx/openembedded/build/tmp/work/cairo-1.2.6-r0/cairo-1.2.6/configure:
line 25429: --exists: command not found
--
/home/leon/sandbox/ixp4xx/openembedded/build/tmp/work/cairo-1.2.6-r0/cairo-1.2.6/configure:
line 25429: --exists: command not found
configure: WARNING: Could not find libpng in the pkg-config search path
---</snippet one>---


Configure was called as follows:


---<snippet two>---
/home/leon/sandbox/ixp4xx/openembedded/build/tmp/work/cairo-1.2.6-r0/cairo-1.2.6/configure
\
                    --build=x86_64-linux \
                    --host=armeb-linux \
                    --target=armeb-linux \
                    --prefix=/usr \
                    --exec_prefix=/usr \
                    --bindir=/usr/bin \
                    --sbindir=/usr/sbin \
                    --libexecdir=/usr/libexec \
                    --datadir=/usr/share \
                    --sysconfdir=/etc \
                    --sharedstatedir=/usr/com \
                    --localstatedir=/var \
                    --libdir=/usr/lib \
                    --includedir=/usr/include \
                    --oldincludedir=/usr/include \
                    --infodir=/usr/share/info \
                    --mandir=/usr/share/man \
                        --without-x --disable-xlib --disable-quartz
--disable-xcb --disable-win32 --disable-glitz --disable-ps
--disable-pdf
--disable-atsui --disable-gtk-doc --enable-png --enable-freetype
---</snippet two>---

Regards,
-- 
Leon