[binutils-gdb] Fix build with GNU Make 3.81

[gdb-buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 1ee7b812e778e4fddcfaa5f0be023dfdfb5a4d6e ***

commit 1ee7b812e778e4fddcfaa5f0be023dfdfb5a4d6e
Author:     Bernd Edlinger <bernd.edlinger@hotmail.de>
AuthorDate: Fri Dec 13 17:21:21 2019 +0100
Commit:     Bernd Edlinger <bernd.edlinger@hotmail.de>
CommitDate: Thu Dec 19 20:18:32 2019 +0100

    Fix build with GNU Make 3.81
    
    GNU Make 3.81 is apparently confused when the same
    source file is processed by a pattern rule and an
    explicit rule at the same time with different output file.
    The pattern %.o: ../%.c and alloc-ipa.o: ../alloc.c
    both have the source ../alloc.c but two independent
    object files alloc.o and alloc-ipa.o, so
    while building gdbserver I see the following message:
    
    make[4]: Circular alloc-ipa.o <- ../alloc.c dependency dropped.
      CXX    alloc-ipa.o
    g++: warning: '-x c++' after last input file has no effect
    g++: fatal error: no input files
    compilation terminated.
    
    In the make debug output I see the pattern is first correct:
    
    alloc-ipa.o: ../alloc.c | config.h build-gnulib-gdbserver/import/string.h
            $(IPAGENT_COMPILE) $(WARN_CFLAGS_NO_FORMAT) $<
            $(POSTCOMPILE)
    
    But after the "Circular" dependency is dropped, the pattern
    is changed to:
    
    alloc-ipa.o: | config.h build-gnulib-gdbserver/import/string.h
            $(IPAGENT_COMPILE) $(WARN_CFLAGS_NO_FORMAT) $<
            $(POSTCOMPILE)
    
    So indeed now $< is empty, and the build step fails.
    
    This happens only when alloc.o needs to be built, when alloc.o
    was already built, the build succeeds, but it takes often
    several attempts until the build succeeds.
    By rewriting the alloc-ipa.c: ../alloc.c rule into a pattern
    rule, the problem goes away.
    
    While already at it, this patch removes also the
    $(WARN_CFLAGS_NO_FORMAT) from the build rule, which is just a
    copy/paste thing that is not necessary for alloc.c at all.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index ecc3db53eb..8ab1f07b87 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,7 @@
+2019-12-16  Bernd Edlinger  <bernd.edlinger@hotmail.de>
+
+	* Makefile.in: Fix build with GNU Make 3.81
+
 2019-12-16  Tom Tromey  <tromey@adacore.com>
 
 	* server.c (get_exec_file): Constify result.
diff --git a/gdb/gdbserver/Makefile.in b/gdb/gdbserver/Makefile.in
index 10e004039f..9e8c213472 100644
--- a/gdb/gdbserver/Makefile.in
+++ b/gdb/gdbserver/Makefile.in
@@ -580,10 +580,6 @@ ax.o: ax.c
 	$(COMPILE) $(WARN_CFLAGS_NO_FORMAT) $<
 	$(POSTCOMPILE)
 
-alloc-ipa.o: ../alloc.c
-	$(IPAGENT_COMPILE) $(WARN_CFLAGS_NO_FORMAT) $<
-	$(POSTCOMPILE)
-
 # Rules for objects that go in the in-process agent.
 
 arch/%-ipa.o: ../arch/%.c
@@ -602,6 +598,10 @@ gdbsupport/%-ipa.o: ../gdbsupport/%.c
 	$(IPAGENT_COMPILE) $<
 	$(POSTCOMPILE)
 
+%-ipa.o: ../%.c
+	$(IPAGENT_COMPILE) $<
+	$(POSTCOMPILE)
+
 # Note: Between two matching pattern rules, GNU Make 3.81 chooses the first one.
 # Therefore, this one needs to be before "%.o: %.c" for it to be considered for
 # files such as linux-amd64-ipa.o generated from linux-amd64-ipa.c.