in math.h make lgamma_r and non-double bessel _GNU_SOURCE only

long double and float bessel functions are no longer xsi extensions

src/math/lgamma.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include "libm.h"
 
 double lgamma(double x)

src/math/lgammaf.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include "libm.h"
 
 float lgammaf(float x)

src/math/lgammal.c

@@ -85,6 +85,7 @@
  *
  */
 
+#define _GNU_SOURCE
 #include "libm.h"
 
 long double lgammal(long double x)