LibM: Add M_SQRT2 and M_SQRT1_2

Author: https://github.com/bugaevc
Commit: https://github.com/SerenityOS/serenity/commit/a449a0b9774
Pull-request: https://github.com/SerenityOS/serenity/pull/2362
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/linusg

Libraries/LibM/math.h

@@ -37,6 +37,8 @@ __BEGIN_DECLS
 #define M_TAU (M_PI * 2)
 #define M_LN2 0.69314718055995
 #define M_LN10 2.30258509299405
+#define M_SQRT2 1.4142135623730951
+#define M_SQRT1_2 0.7071067811865475
 
 double acos(double);
 float acosf(float);