newlib: don't define non-thread-safe versions of getc, putc

getc, getchar, putc, putchar were defined both as functions and as
macros. The macro versions are not thread safe, and should not be used
in multithreaded applications.

Upstream fix: b0f271d1db

components/newlib/include/stdio.h

@@ -696,8 +696,10 @@ _ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
 
 #ifndef __CYGWIN__
 #ifndef lint
+#ifdef __SINGLE_THREAD__
 #define	getc(fp)	__sgetc_r(_REENT, fp)
 #define putc(x, fp)	__sputc_r(_REENT, x, fp)
+#endif /* __SINGLE_THREAD__ */
 #endif /* lint */
 #endif /* __CYGWIN__ */
 
@@ -714,8 +716,10 @@ _ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
 
 #endif /* !__CUSTOM_FILE_IO__ */
 
+#ifdef __SINGLE_THREAD__
 #define	getchar()	getc(stdin)
 #define	putchar(x)	putc(x, stdout)
+#endif /* __SINGLE_THREAD__ */
 
 #ifndef __STRICT_ANSI__
 #define	getchar_unlocked()	getc_unlocked(stdin)