replace JNR_PCRE with JNI_PCRE

com.oracle.truffle.r.native/fficall/Makefile

com.oracle.truffle.r.native/fficall/src/jni/Rinternals.c

com.oracle.truffle.r.native/fficall/src/jni/pcre_fastr.c

com.oracle.truffle.r.native/fficall/src/jni/rfficall.c

com.oracle.truffle.r.native/gnur/Makefile.libs

...fi/src/com/oracle/truffle/r/runtime/ffi/jnr/JNI_PCRE.java

...com/oracle/truffle/r/runtime/ffi/jnr/JNR_RFFIFactory.java

mx.fastr/mx_fastr.py

mx.fastr/mx_find_pcre.py