tools/nolibc: make the default target build the headers

The help in "make -C tools" enumerates nolibc as a valid target so we
must at least make it do something. Let's make it do the equivalent
of "make headers" in that it will prepare a sysroot with the arch's
headers, but will not install the kernel's headers. This is the
minimum some tools will need when built with a full-blown toolchain
anyway.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/Makefile

@@ -78,6 +78,9 @@ bpf/%: FORCE
 libapi: FORCE
 	$(call descend,lib/api)
 
+nolibc: FORCE
+	$(call descend,include/nolibc)
+
 nolibc_%: FORCE
 	$(call descend,include/nolibc,$(patsubst nolibc_%,%,$@))
 

tools/include/nolibc/Makefile

@@ -29,7 +29,7 @@ all_files := ctype.h errno.h nolibc.h signal.h std.h stdio.h stdlib.h string.h \
              sys.h time.h types.h unistd.h
 
 # install all headers needed to support a bare-metal compiler
-all:
+all: headers
 
 # Note: when ARCH is "x86" we concatenate both x86_64 and i386
 headers: