Modify ctype.h headers to test for non-GNU inline semantics correctly

GCC and Clang will not define __GNUC_STDC_INLINE__ when compiling C++, so this
macro currently implies regular C++ inline semantics in C++. This may cause
the compiler to emit an external definition of the function, which will cause
link errors when compiling with -fvisibility=hidden; see e.g. crbug.com/481902.

To fix this, also test the __cplusplus macro when deciding whether to assume
non-GNU inline semantics.

Change-Id: Icbd1f42279c2f65610e62f21d4a0a09d3b0e091c
1 file changed