libcurl: fix build on uncommon architectures

Since the bump to 7.55.0, libcurl fails to build on a number of
uncommon architectures (ARC, OpenRISC, etc.). This is due to upstream
commit 73a2fcea0b4adea6ba342cd7ed1149782c214ae3 ("includes: remove
curl/curlbuild.h and curl/curlrules.h"), which makes libcurl rely on
more architecture-specific related defines in include/curl/system.h.

This commit therefore adds a patch that fixes the 32-bit vs. 64-bit
detection for all architecture, using gcc's __SIZEOF_LONG__
definition. It has been tested successfully with test-pkg on all 47
toolchain configurations.

Fixes:

  http://autobuild.buildroot.net/results/bf26c08cf3267214278674472f931603f69951ae/


  (and many similar issues)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>