[newlib-cygwin] newlib: don't use __visibility__ attrribute on Cygwin

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=054ff18f5f7fd3baa696656949d4cad74e465cf7

commit 054ff18f5f7fd3baa696656949d4cad74e465cf7
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Wed Aug 8 10:44:38 2018 +0200

    newlib: don't use __visibility__ attrribute on Cygwin
    
    gcc doesn't support visibility attribute on PE/COFF platforms
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 newlib/libm/common/math_config.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/newlib/libm/common/math_config.h b/newlib/libm/common/math_config.h
index cca682e..f28c52b 100644
--- a/newlib/libm/common/math_config.h
+++ b/newlib/libm/common/math_config.h
@@ -235,17 +235,22 @@ eval_as_double (double x)
 }
 
 #ifdef __GNUC__
-# define HIDDEN __attribute__ ((__visibility__ ("hidden")))
 # define NOINLINE __attribute__ ((noinline))
 # define likely(x) __builtin_expect (!!(x), 1)
 # define unlikely(x) __builtin_expect (x, 0)
 #else
-# define HIDDEN
 # define NOINLINE
 # define likely(x) (x)
 # define unlikely(x) (x)
 #endif
 
+/* gcc emitting PE/COFF doesn't support visibility */
+#if defined (__GNUC__) && !defined (__CYGWIN__)
+# define HIDDEN __attribute__ ((__visibility__ ("hidden")))
+#else
+# define HIDDEN
+#endif
+
 /* Error handling tail calls for special cases, with a sign argument.
    The sign of the return value is set if the argument is non-zero.  */