mesa: Fix compiler warnings

Add explicit casts, fix constant types, fix variable types.
Fixes about 340 warnings in MSFT Visual Studio.
diff --git a/src/mesa/shader/prog_parameter.c b/src/mesa/shader/prog_parameter.c
index 5822510..d4970c4 100644
--- a/src/mesa/shader/prog_parameter.c
+++ b/src/mesa/shader/prog_parameter.c
@@ -209,7 +209,7 @@
 {
    /* first check if this is a duplicate constant */
    GLint pos;
-   for (pos = 0; pos < paramList->NumParameters; pos++) {
+   for (pos = 0; pos < (GLint)paramList->NumParameters; pos++) {
       const GLfloat *pvals = paramList->ParameterValues[pos];
       if (pvals[0] == values[0] &&
           pvals[1] == values[1] &&