Build: Fix --disable-threads breaking the building of shared libs.

This is broken in the releases 5.2.6 to 5.4.2. A workaround
for these releases is to pass EGREP='grep -E' as an argument
to configure in addition to --disable-threads.

The problem appeared when m4/ax_pthread.m4 was updated in
the commit 6629ed929cc7d45a11e385f357ab58ec15e7e4ad which
introduced the use of AC_EGREP_CPP. AC_EGREP_CPP calls
AC_REQUIRE([AC_PROG_EGREP]) to set the shell variable EGREP
but this was only executed if POSIX threads were enabled.
Libtool code also has AC_REQUIRE([AC_PROG_EGREP]) but Autoconf
omits it as AC_PROG_EGREP has already been required earlier.
Thus, if not using POSIX threads, the shell variable EGREP
would be undefined in the Libtool code in configure.

ax_pthread.m4 is fine. The bug was in configure.ac which called
AX_PTHREAD conditionally in an incorrect way. Using AS_CASE
ensures that all AC_REQUIREs get always run.

Thanks to Frank Busse for reporting the bug.
Fixes: https://github.com/tukaani-project/xz/issues/45

diff --git a/configure.ac b/configure.ac
index d8811b9bd471f96a581f54bd9c672ff5d211e0ef..e3314a9da114d4070027079b6e499ef68718a4b2 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -611,8 +611,8 @@ AM_PROG_CC_C_O
 AM_PROG_AS
 AC_USE_SYSTEM_EXTENSIONS
 
-case $enable_threads in
-       posix)
+AS_CASE([$enable_threads],
+       [posix], [
                echo
                echo "POSIX threading support:"
                AX_PTHREAD([:]) dnl We don't need the HAVE_PTHREAD macro.
@@ -643,19 +643,19 @@ case $enable_threads in
                        `CLOCK_MONOTONIC' is declared in <time.h>.])], [],
                        [[#include <time.h>]])
                CFLAGS=$OLD_CFLAGS
-               ;;
-       win95)
+       ],
+       [win95], [
                AC_DEFINE([MYTHREAD_WIN95], [1], [Define to 1 when using
                        Windows 95 (and thus XP) compatible threads.
                        This avoids use of features that were added in
                        Windows Vista.])
-               ;;
-       vista)
+       ],
+       [vista], [
                AC_DEFINE([MYTHREAD_VISTA], [1], [Define to 1 when using
                        Windows Vista compatible threads. This uses
                        features that are not available on Windows XP.])
-               ;;
-esac
+       ]
+)
 AM_CONDITIONAL([COND_THREADS], [test "x$enable_threads" != xno])
 
 echo