saivpp compilation warnings

[yue-fred-gao]

saivpp vppxlate produces a lot of warnings. We need to fix them. Here are the flags we need to turn on to check on those warnings.
-Wno-unused-function
-Wno-sign-conversion
-Wno-conversion
-Wno-unused-variable
-Wno-sign-compare
-Wno-shadow
-Wno-discarded-qualifiers
-Wno-redundant-decls
-Wno-cast-align
-Wno-pointer-sign
-Wno-stringop-truncation
-Wno-cast-qual