Easier to just make g-ir-scanner skip this header via #ifndef __GI_SCANNER__
than maintain different sets of headers in the meson.build file.

Warning: Gst: symbol="rint": Unknown namespace for symbol "rint"
Warning: Gst: symbol="rintf": Unknown namespace for symbol "rintf"
Warning: Gst: symbol="isnan": Unknown namespace for symbol "isnan"
Part-of: <!579>