Avoid Microsoft compiler warnings (#51331).

While clang's sanitizer recommends a cast to unsigned for safe
negation (to handle -INT_MIN), both MSVC and Visualc emit warning
C4146 if an unsigned value gets negated.

* include/freetype/internal/ftcalc.h (NEG_LONG, NEG_INT32),
src/base/ftcalc.c (FT_MOVE_SIGN): Replace negation with a
subtraction.

ChangeLog

@@ -1,3 +1,15 @@
+2017-06-28  Ben Wagner  <bungeman@google.com>
+
+	Avoid Microsoft compiler warnings (#51331).
+
+	While clang's sanitizer recommends a cast to unsigned for safe
+	negation (to handle -INT_MIN), both MSVC and Visualc emit warning
+	C4146 if an unsigned value gets negated.
+
+	* include/freetype/internal/ftcalc.h (NEG_LONG, NEG_INT32),
+	src/base/ftcalc.c (FT_MOVE_SIGN): Replace negation with a
+	subtraction.
+
 2017-06-27  Werner Lemberg  <wl@gnu.org>
 
 	* src/cff/cffparse.c (do_fixed): Fix typo.

include/freetype/internal/ftcalc.h

@@ -424,7 +424,7 @@ FT_BEGIN_HEADER
 #define MUL_LONG( a, b )                             \
           (FT_Long)( (FT_ULong)(a) * (FT_ULong)(b) )
 #define NEG_LONG( a )                                \
-          (FT_Long)( -(FT_ULong)(a) )
+          (FT_Long)( (FT_ULong)0 - (FT_ULong)(a) )
 
 #define ADD_INT32( a, b )                               \
           (FT_Int32)( (FT_UInt32)(a) + (FT_UInt32)(b) )
@@ -433,7 +433,7 @@ FT_BEGIN_HEADER
 #define MUL_INT32( a, b )                               \
           (FT_Int32)( (FT_UInt32)(a) * (FT_UInt32)(b) )
 #define NEG_INT32( a )                                  \
-          (FT_Int32)( -(FT_UInt32)(a) )
+          (FT_Int32)( (FT_UInt32)0 - (FT_UInt32)(a) )
 
 
 FT_END_HEADER

src/base/ftcalc.c

@@ -74,7 +74,7 @@
   FT_BEGIN_STMNT                         \
     if ( x < 0 )                         \
     {                                    \
-      x_unsigned = -x_unsigned;          \
+      x_unsigned = 0u - (x_unsigned);    \
       s          = -s;                   \
     }                                    \
   FT_END_STMNT