define jbyte as signed char

[Yuri Dario]

In the OS/2 sdk, jni_mh.h defines the following types:

#ifdef GNUC
typedef int jint;
typedef int64_t jlong;
typedef signed char jbyte;
#else
typedef long jint;
typedef int64 jlong;
typedef signed char jbyte;
#endif

but the GNUC defines are different from default ones on other platforms.

When building Apache OpenOffice, errors are issued because there isn't a direct cast from signed char to char, even if signed char is the default setting (they are treated as different types).