Add symbolic name for additional compiler warnings

Norcroft's `-We` option suppresses warnings about casts between function
pointers and non-function objects.

Norcroft's `-Wn` option suppresses warnings about implicit narrowing casts.

GCC doesn't have equivalents to these warnings, so they expand to an empty
string if that's the selected compiler.

GNUmakefiles/StdTools

@@ -191,6 +191,8 @@ C++FLAGS    += -mlibscl
 LDFLAGS     += -mlibscl
 endif
 C_NOWARN_ASSIGNMENT_AS_CONDITION := -Wno-parentheses
+C_NOWARN_FUNCCAST :=
+C_NOWARN_NARROWING_CAST :=
 C_NOWARN_NON_ANSI_INCLUDES :=
 
 else
@@ -211,6 +213,8 @@ C_NO_FNAMES := -ff
 C_FNAMES    := -fn
 C_MODULE    := -zM
 C_NOWARN_ASSIGNMENT_AS_CONDITION := -Wa
+C_NOWARN_FUNCCAST := -We
+C_NOWARN_NARROWING_CAST := -Wn
 C_NOWARN_NON_ANSI_INCLUDES := -Wp
 
 endif

Makefiles/StdTools

@@ -127,6 +127,8 @@ C_NO_FNAMES := -ff
 C_FNAMES    := -fn
 C_MODULE    := -zM
 C_NOWARN_ASSIGNMENT_AS_CONDITION := -Wa
+C_NOWARN_FUNCCAST := -We
+C_NOWARN_NARROWING_CAST := -Wn
 C_NOWARN_NON_ANSI_INCLUDES := -Wp
 
 #