Use "-I." in directories holding Bison parsers, for Oracle compilers.

With the Oracle Developer Studio 12.6 compiler, #line directives alter
the current source file location for purposes of #include "..."
directives.  Hence, a VPATH build failed with 'cannot find include file:
"specscanner.c"'.  With two exceptions, parser-containing directories
already add "-I. -I$(srcdir)"; eliminate the exceptions.  Back-patch to
9.6 (all supported versions).

src/backend/utils/adt/Makefile

@@ -8,6 +8,8 @@ subdir = src/backend/utils/adt
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
+
 # keep this list arranged alphabetically or it gets to be a mess
 OBJS = \
 	acl.o \

src/test/isolation/Makefile

@@ -9,7 +9,8 @@ subdir = src/test/isolation
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-override CPPFLAGS := -I$(srcdir) -I$(libpq_srcdir) -I$(srcdir)/../regress $(CPPFLAGS)
+override CPPFLAGS := -I. -I$(srcdir) -I$(libpq_srcdir) \
+	-I$(srcdir)/../regress $(CPPFLAGS)
 
 OBJS = \
 	$(WIN32RES) \