gdb/Makefile: add gcore to the 'all' target dependency list

The gcore script is initially generated by the configure process, just
like gdb-gdb.gdb and gdb-gdb.py.  However if the gdb/gcore.in input
source is modified then 'make all' in the gdb/ directory does not
regenerate the gcore script.

This is different than the gdb-gdb.gdb and gdb-gdb.py files, if their
input is updated then 'make all' will regenerate these files.

The difference is that for gdb-gdb.* there is an explicit dependency
between the 'all' target and the generated file, this dependency is
missing for gcore.

This commit adds the dependency.  Now, if gcore.in is changed, running
'make all' will regenerate the gcore script.

There is no change in _what_ is generated after this commit.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdb/Makefile.in

@@ -1938,7 +1938,7 @@ generated_files = \
 # Flags needed to compile Python code
 PYTHON_CFLAGS = @PYTHON_CFLAGS@
 
-all: gdb$(EXEEXT) $(CONFIG_ALL) gdb-gdb.py gdb-gdb.gdb
+all: gdb$(EXEEXT) $(CONFIG_ALL) gdb-gdb.py gdb-gdb.gdb gcore
 	@$(MAKE) $(FLAGS_TO_PASS) DO=all "DODIRS=$(SUBDIRS)" subdir_do
 
 # Rule for compiling .c files in the top-level gdb directory.