mesa: fix double->float assignment warnings, int/uint comparison warnings

Reported by Karl Schultz.
diff --git a/src/mesa/shader/program.c b/src/mesa/shader/program.c
index 6b8d94e..3e86d0a 100644
--- a/src/mesa/shader/program.c
+++ b/src/mesa/shader/program.c
@@ -580,7 +580,7 @@
    for (i = 0; i < prog->NumInstructions; i++) {
       struct prog_instruction *inst = prog->Instructions + i;
       if (inst->BranchTarget > 0) {
-         if (inst->BranchTarget > start) {
+         if (inst->BranchTarget > (GLint) start) {
             inst->BranchTarget -= count;
          }
       }