Move some POSIX math functions out of _USE_GNU/_USE_BSD.

The signgam global and the j0/j1/jn and y0/y1/yn functions are POSIX.

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/math.h.html

Change-Id: I802997a2060a011a777c2b641f28c1d58dfe49ed
diff --git a/libc/include/math.h b/libc/include/math.h
index 1afef4c..37aa2cc 100644
--- a/libc/include/math.h
+++ b/libc/include/math.h
@@ -81,6 +81,8 @@
 #define HUGE MAXFLOAT
 #endif
 
+extern int signgam;
+
 /*
  * Most of these functions depend on the rounding mode and have the side
  * effect of raising floating-point exceptions, so they are not declared
@@ -297,6 +299,13 @@
 long double tgammal(long double) __INTRODUCED_IN(21);
 long double truncl(long double);
 
+double j0(double);
+double j1(double);
+double jn(int, double);
+double y0(double);
+double y1(double);
+double yn(int, double);
+
 #define M_E		2.7182818284590452354	/* e */
 #define M_LOG2E		1.4426950408889634074	/* log 2e */
 #define M_LOG10E	0.43429448190325182765	/* log 10e */
@@ -314,13 +323,6 @@
 #define MAXFLOAT	((float)3.40282346638528860e+38)
 
 #if defined(__USE_BSD) || defined(__USE_GNU)
-extern int signgam;
-double j0(double);
-double j1(double);
-double jn(int, double);
-double y0(double);
-double y1(double);
-double yn(int, double);
 double gamma(double);
 double scalb(double, double);
 double drem(double, double);