feat: libc - add strndup, scandir, alphasort, usleep, ftruncate, M_PI constants

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_018Ae69wJS7sueQMUwNxV3nX

programs/include/libc/math.h

@@ -11,6 +11,24 @@ extern "C" {
 #define INFINITY  __builtin_inff()
 #define NAN       __builtin_nanf("")
 
+/*
+ * X/Open math constants. Not in ISO C, but ported code assumes them freely
+ * (NetSurf's about:chart uses M_PI and M_PI_2).
+ */
+#define M_E        2.7182818284590452354
+#define M_LOG2E    1.4426950408889634074
+#define M_LOG10E   0.43429448190325182765
+#define M_LN2      0.69314718055994530942
+#define M_LN10     2.30258509299404568402
+#define M_PI       3.14159265358979323846
+#define M_PI_2     1.57079632679489661923
+#define M_PI_4     0.78539816339744830962
+#define M_1_PI     0.31830988618379067154
+#define M_2_PI     0.63661977236758134308
+#define M_2_SQRTPI 1.12837916709551257390
+#define M_SQRT2    1.41421356237309504880
+#define M_SQRT1_2  0.70710678118654752440
+
 /* C99 floating-point classification. */
 #define FP_NAN       0
 #define FP_INFINITE  1