Makeconfig: Use $(error ...) to output error message

Being not familiar with the glibc repository, I typed "make" inside some
subdirectory that has a Makefile, and was met with:

    $ make
    ../Makeconfig:42: *** missing separator.  Stop.

At Makeconfig:42, we have:

    objdir must be defined by the build-directory Makefile.

Change that to use $(error ...), which I guess was the original
intention.  The result is:

    $ make
    ../Makeconfig:42: *** objdir must be defined by the build-directory Makefile.  Stop.

1 files changed, 1 insertions, 1 deletions

diff --git a/Makeconfig b/Makeconfig
index ac567caddc..dfda418aac 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -39,7 +39,7 @@ objpfx := $(patsubst %//,%/,$(objdir)/$(subdir)/)
 common-objpfx = $(objdir)/
 common-objdir = $(objdir)
 else
-objdir must be defined by the build-directory Makefile.
+$(error objdir must be defined by the build-directory Makefile)
 endif
 
 # Root of the sysdeps tree.