gallium: Integrate util_half with scons.

src/gallium/auxiliary/SConscript

@@ -143,7 +143,9 @@ source = [
     'util/u_format_s3tc.c',
     'util/u_format_table.c',
     'util/u_format_tests.c',
+    'util/u_gctors.cpp',
     'util/u_gen_mipmap.c',
+    'util/u_half.c',
     'util/u_handle_table.c',
     'util/u_hash.c',
     'util/u_hash_table.c',

src/gallium/include/pipe/p_compiler.h

@@ -74,6 +74,7 @@ typedef unsigned char boolean;
 #define FALSE false
 #endif
 
+typedef unsigned short half;
 
 /* Function inlining */
 #ifndef INLINE