Capture pkg-config output even if only one component returned

[kkopachev]

Changing pkg-config output parser in case it returns only one component
(only -I or only -L)

Currently an issue with libtiff in official python container:

> docker run --rm -it --entrypoint=bash python:3
# pkg-config --libs-only-L libtiff-4 --cflags-only-I libtiff-4
 -I/usr/include/x86_64-linux-gnu 
# pip install pillow --global-option="build_ext" --global-option="--disable-zlib" \
 --global-option="build_ext" --global-option="--disable-jpeg" \
 --global-option="build_ext" --global-option="--enable-tiff"

...
    The headers or library files could not be found for tiff,
    which was requested by the option flag --enable-tiff

[kkopachev]

Fixed by #3395