loadperf: Add UnloadPerfCounterTextStrings stubs.

include/Makefile.in

diff --git a/include/Makefile.in b/include/Makefile.in
index 8f004f2..8604b8f 100644
--- a/include/Makefile.in
+++ b/include/Makefile.in
@@ -259,6 +259,7 @@
 	lmuse.h \
 	lmuseflg.h \
 	lmwksta.h \
+	loadperf.h \
 	lzexpand.h \
 	mapi.h \
 	mapicode.h \