[LyX/master] Fix generation of lyx_commit_hash.h

[Jean-Marc Lasgouttes]

commit e86cc0135ab6c67938cf097514891ccf33c74e17
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Tue Mar 10 19:11:48 2015 +0100

    Fix generation of lyx_commit_hash.h
    
    Now version.o is not recompiled on already built tree.

diff --git a/src/Makefile.am b/src/Makefile.am
index 9b6b538..6df5858 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -305,11 +305,23 @@ HEADERFILESCORE = \
 STANDALONEFILES = \
        Layout.cpp
 
-.PHONY: lyx_commit_hash.h
 
-lyx_commit_hash.h:
-       $(AM_V_GEN)hash=`cd "$(top_srcdir)" && git log -1 --pretty=format:%H 
2>/dev/null || echo none` ; \
-        sed s/@LYX_GIT_COMMIT_HASH@/$$hash/ "$(srcdir)"/lyx_commit_hash.h.in 
>$@
+.PHONY: update_commit_hash
+
+LCH_V_GEN = $(lch__v_GEN_@AM_V@)
+lch__v_GEN_ = $(lch__v_GEN_@AM_DEFAULT_V@)
+lch__v_GEN_0 = @echo "  GEN      lyx_commit_hash.h";
+lch__v_GEN_1 =
+
+update_commit_hash:
+       rm -f hash-temp \
+       $(LCH_V_GEN)hash=`cd "$(top_srcdir)" && git log -1 --pretty=format:%H 
2>/dev/null || echo none` ; \
+       sed s/@LYX_GIT_COMMIT_HASH@/$$hash/ "$(srcdir)"/lyx_commit_hash.h.in 
>hash-temp ; \
+       cmp -s lyx_commit_hash.h hash-temp || cp hash-temp lyx_commit_hash.h ; \
+       rm -f hash-temp
+
+lyx_commit_hash.h: update_commit_hash
+
 BUILT_SOURCES += lyx_commit_hash.h
 CLEANFILES += lyx_commit_hash.h