[PATCH] [BUILD] fix parallel build

["Yann E. MORIN" <yann.morin.1998@xxxxxxx>]

When neither token.h nor token_var.h exist, and we are building in
parallel, it is possible that make will spawn two mktokens at roughly
the same time, because of two different rules, one that needs token.h ad
another that need token_vars.h.

For example, make can have a dependency chain toward just token.h, from
syntax.c, and another dependency chain toweard token_vars.h from the
generic BUILT_SOURCES.

So, make will "quickly" decide that it needs token.h, then spawn
mktoken. A bit later, while that mktoken still runs but hasn't yet
created token_vars.h, make will need it, and thus spawn a second
mktoken.

While the second one runs, the first terminates. However, the token.h it
had generated has been in the meantime overwritten by the second mktoken
that is still generating it, and token.h is still empty.

But make proceeds to the rule that required token.h in the first place,
and the still-empty token.h gets icluded from a C file, and the build
fails because of missing defines.

For example:
    http://autobuild.buildroot.org/results/fc4/fc4e4ab47455ac47dd4a3a60083cec2848e74dbb/build-end.log

Fix that by serialising both headers.

Reported-by: Baruch Siach <baruch@xxxxxxxxxx>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@xxxxxxx>
Cc: Baruch Siach <baruch@xxxxxxxxxx>
---
 src/Makefile.am | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Makefile.am b/src/Makefile.am
index 46399c7..5bf5a52 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -44,7 +44,8 @@ EXTRA_DIST = \
 	mktokens mkbuiltins builtins.def.in mkinit.c \
 	mknodes.c nodetypes nodes.c.pat mksyntax.c mksignames.c
 
-token.h token_vars.h: mktokens
+token_vars.h: token.h
+token.h: mktokens
 	$(SHELL) $^
 
 builtins.def: builtins.def.in $(top_builddir)/config.h
-- 
2.14.1

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