Add support for the Little CMS fast float plugin

On a sample of JPEGs, it improved loading speed from ~0.26s to ~0.15s.

Unfortunately, it isn't normally installed.

fiv.c

@@ -43,6 +43,11 @@
 #include "fiv-thumbnail.h"
 #include "fiv-view.h"
 
+#ifdef HAVE_LCMS2_FAST_FLOAT
+#include <lcms2.h>
+#include <lcms2_fast_float.h>
+#endif  // HAVE_LCMS2_FAST_FLOAT
+
 // --- Utilities ---------------------------------------------------------------
 
 static void exit_fatal(const char *format, ...) G_GNUC_PRINTF(1, 2);
@@ -2382,6 +2387,11 @@ on_app_handle_local_options(G_GNUC_UNUSED GApplication *app,
 		return 0;
 	}
 
+	// TODO(p): Use Little CMS with contexts instead.
+#ifdef HAVE_LCMS2_FAST_FLOAT
+	cmsPlugin(cmsFastFloatExtensions());
+#endif  // HAVE_LCMS2_FAST_FLOAT
+
 	// Normalize all arguments to URIs, and run thumbnailing modes first.
 	for (gsize i = 0; o.args && o.args[i]; i++) {
 		GFile *resolved = g_file_new_for_commandline_arg(o.args[i]);