llvmpipe: Allow floating types without sign.

With the meaning that all values are assumed to be positive.

src/gallium/drivers/llvmpipe/lp_bld_type.c

@@ -29,13 +29,13 @@
 #include "util/u_debug.h"
 
 #include "lp_bld_type.h"
+#include "lp_bld_const.h"
 
 
 LLVMTypeRef
 lp_build_elem_type(union lp_type type)
 {
    if (type.floating) {
-      assert(type.sign);
       switch(type.width) {
       case 32:
          return LLVMFloatType();

src/gallium/drivers/llvmpipe/lp_bld_type.h

@@ -73,7 +73,8 @@ union lp_type {
       /** 
        * Whether it can represent negative values or not.
        *
-       * Floating point values should always have this bit set.
+       * If this is not set for floating point, it means that all values are
+       * assumed to be positive.
        */
       unsigned sign:1;