debuginfod: PR28034 - client-side %-escape url characters

debuginfod: PR28034 - client-side %-escape url characters

When requesting some source files, some URL-inconvenient chars
sometimes pop up.  Example from f33 libstdc++:
/buildid/44d8485cb75512c2ca5c8f70afbd475cae30af4f/source/usr/src/debug/
gcc-10.3.1-1.fc33.x86_64/obj-x86_64-redhat-linux/x86_64-redhat-linux/
libstdc++-v3/src/c++11/../../../../../libstdc++-v3/src/c++11/
condition_variable.cc
As this URL is passed into debuginfod's handler_cb, it appears that the
+ signs are helpfully unescaped to spaces by libmicrohttpd, which
'course breaks everything.
In order to ensure the server properly parses urls such as this one,
%-escape characters on the client side so that the correct url
is preserved and properly processed on the server side.

https://sourceware.org/bugzilla/show_bug.cgi?id=28034

Signed-off-by: Noah Sanci <nsanci@redhat.com>