[liba] Replace the gamma extern constant file by the open bsd file

Change-Id: I11b6a6912aff05fc31a4a75c27ee5ff3bf5e2dbd

liba/Makefile

@@ -36,10 +36,10 @@ objs += $(addprefix liba/src/external/openbsd/, \
   s_floorf.o \
   s_roundf.o \
   s_scalbnf.o \
+  s_signgam.o \
   s_sinf.o \
   s_tanf.o \
   w_lgammaf.o \
-  gamma_extern_variable.o\
 )
 
 liba/src/external/openbsd/%.o: CFLAGS += -Iliba/src/external/openbsd/include -Wno-parentheses -Wno-implicit-function-declaration

liba/src/external/openbsd/gamma_extern_variable.c

@@ -1,3 +0,0 @@
-/* The openbsd w_lgamma.c requieres at linking a symbol signgam */
-
-int signgam;

liba/src/external/openbsd/s_signgam.c

@@ -0,0 +1,4 @@
+/*	$OpenBSD: s_signgam.c,v 1.2 2015/01/20 04:41:01 krw Exp $	*/
+#include "math.h"
+#include "math_private.h"
+int signgam = 0;