common: rename getc() to getchar()

The sandbox is built with the SDL2 library with invokes the X11 library
which in turn calls getc(). But getc() in glibc is defined as

    int getc(FILE *)

This does not match our definition.

    int getc(void)

The sandbox crashes when called with parameter -l.

Rename our library symbol getc() to getchar().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/stdio.h

@@ -5,7 +5,7 @@
 #include <linux/compiler.h>
 
 /* stdin */
-int getc(void);
+int getchar(void);
 int tstc(void);
 
 /* stdout */