math: remove libc.h include from libm.h

libc.h is only for weak_alias so include it directly where it is used

src/internal/libm.h

@@ -19,8 +19,6 @@
 #include <complex.h>
 #include <endian.h>
 
-#include "libc.h"
-
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
 #elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER == __LITTLE_ENDIAN
 union ldshape {

src/math/lgamma_r.c

@@ -79,6 +79,7 @@
  */
 
 #include "libm.h"
+#include "libc.h"
 
 static const double
 two52= 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */

src/math/lgammaf_r.c

@@ -14,6 +14,7 @@
  */
 
 #include "libm.h"
+#include "libc.h"
 
 static const float
 two23= 8.3886080000e+06, /* 0x4b000000 */

src/math/lgammal.c

@@ -87,6 +87,7 @@
 
 #define _GNU_SOURCE
 #include "libm.h"
+#include "libc.h"
 
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
 double __lgamma_r(double x, int *sg);

src/math/signgam.c

-#include "libm.h"
+#include <math.h>
+#include "libc.h"
 
 int __signgam = 0;