cos_tablegen: fix the lack on M_PI

We dont include mathematics.h as the headers get configured by config.h
for the target not the host.
Reviewed-by: Clément Bœsch <ubitux@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/cos_tablegen.c

@@ -56,7 +56,7 @@ int main(int argc, char *argv[])
     printf("#include \"libavcodec/%s\"\n", do_sin ? "rdft.h" : "fft.h");
     for (i = 4; i <= BITS; i++) {
         int m = 1 << i;
-        double freq = 2*M_PI/m;
+        double freq = 2*3.14159265358979323846/m;
         printf("%s(%i) = {\n   ", do_sin ? "SINTABLE" : "COSTABLE", m);
         for (j = 0; j < m/2 - 1; j++) {
             int idx = j > m/4 ? m/2 - j : j;