[cmake] fix build with -DENABLE_MICROHTTP=OFF and without installed libmicrohttpd

[herrnst]

Description

Follow-up to http://trac.kodi.tv/ticket/17131 and #11145

With -DENABLE_MICROHTTPD=OFF, xbmc/network/httprequesthandler/* and xbmc/interfaces/legacy/wsgi/* were still compiled, making the compiler stop with "microhttpd.h not found" fatals. This adds if()'s in the CMakeLists.txt of the affected directories, mimic'ing https://github.com/xbmc/xbmc/blob/Krypton/Makefile.in#L126.

Motivation and Context

Fix build without webserver even when libmicrohttpd isn't installed.

How Has This Been Tested?

Build with -DENABLE_MICROHTTPD={OFF,ON}, with and without libmicrohttpd installed.

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the Code guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have added tests to cover my change
• All new and existing tests passed

[wsnipex]

thanks, looks good

[Jalle19]

Noticed this too while compiling a few days ago, thanks for fixing!

[MartijnKaijser]

@herrnst can you make a PR for Krypton as well?

[herrnst]

Done: #11294