config: fix style issues when source-ing files

Always enclose the sourced file between double-quotes (purely for
consistency; enclosing or not are both allowed by the kconfig language).

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/projects/crosstool"

reporter_comment="Experimental toolchain for ARM cortex-m3 in Thumb-only, noMMU, and newlib."