ctype.h: remove duplicate isdigit() helper

gcc warns a few thousand times about the isdigit() shadow:

include/linux/ctype.h:26:19: warning: declaration of 'isdigit' shadows a built-in function [-Wshadow]

As there is already a compiler builtin, just use that, and make
it clear we do that by defining a macro.  Unfortunately, clang
does not have the isdigit() builtin, so this has to be conditional.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 6e390d58a9f8..5d41dff3f79c 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -64,6 +64,17 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
 /* Attributes */
 #include <linux/compiler_attributes.h>
 
+/* Builtins */
+
+/*
+ * __has_builtin is supported on gcc >= 10, clang >= 3 and icc >= 21.
+ * In the meantime, to support gcc < 10, we implement __has_builtin
+ * by hand.
+ */
+#ifndef __has_builtin
+#define __has_builtin(x) (0)
+#endif
+
 /* Compiler specific macros. */
 #ifdef __clang__
 #include <linux/compiler-clang.h>