*: make "pragma GCC visibility push(hidden)" less ugly

diff --git a/shell/math.h b/shell/math.h
index 195fc20..51dbb56 100644
--- a/shell/math.h
+++ b/shell/math.h
@@ -72,8 +72,10 @@
  * below for the exact things that are available.
  */
 
-#ifndef _SHELL_MATH_
-#define _SHELL_MATH_
+#ifndef SHELL_MATH_H
+#define SHELL_MATH_H 1
+
+PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
 
 #if ENABLE_SH_MATH_SUPPORT_64
 typedef long long arith_t;
@@ -96,4 +98,6 @@
 
 arith_t arith(const char *expr, int *perrcode, arith_eval_hooks_t*);
 
+POP_SAVED_FUNCTION_VISIBILITY
+
 #endif