build: Stop linking pthread (#4695)

Added on commit 137985136 ("Baseline firejail 0.9.28", 2015-08-08).  See
also commit ad6bb83fa ("consolidate makefiles", 2018-03-31).

It is not used anywhere.  And it looks like it has never been used
anywhere:

    $ git log --oneline -Gpthread.h 137985136..master
    $

Issue mentioned by @rusty-snake:
https://github.com/netblue30/firejail/issues/4642#issuecomment-955795463

3 files changed, 1 insertions, 106 deletions

diff --git a/configure b/configure
index 557f5beb2..747769fb1 100755
--- a/configure
+++ b/configure
@@ -1533,52 +1533,6 @@ fi
 
 } # ac_fn_c_try_compile
 
-# ac_fn_c_try_link LINENO
-# -----------------------
-# Try to link conftest.$ac_ext, and return whether this succeeded.
-ac_fn_c_try_link ()
-{
-  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
-  rm -f conftest.$ac_objext conftest$ac_exeext
-  if { { ac_try="$ac_link"
-case "(($ac_try" in
-  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
-  *) ac_try_echo=$ac_try;;
-esac
-eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
-$as_echo "$ac_try_echo"; } >&5
-  (eval "$ac_link") 2>conftest.err
-  ac_status=$?
-  if test -s conftest.err; then
-    grep -v '^ *+' conftest.err >conftest.er1
-    cat conftest.er1 >&5
-    mv -f conftest.er1 conftest.err
-  fi
-  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
-  test $ac_status = 0; } && {
-         test -z "$ac_c_werror_flag" ||
-         test ! -s conftest.err
-       } && test -s conftest$ac_exeext && {
-         test "$cross_compiling" = yes ||
-         test -x conftest$ac_exeext
-       }; then :
-  ac_retval=0
-else
-  $as_echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
-
-        ac_retval=1
-fi
-  # Delete the IPA/IPO (Inter Procedural Analysis/Optimization) information
-  # created by the PGI compiler (conftest_ipa8_conftest.oo), as it would
-  # interfere with the next link command; also delete a directory that is
-  # left behind by Apple's compiler.  We do this before executing the actions.
-  rm -rf conftest.dSYM conftest_ipa8_conftest.oo
-  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
-  as_fn_set_status $ac_retval
-
-} # ac_fn_c_try_link
-
 # ac_fn_c_try_cpp LINENO
 # ----------------------
 # Try to preprocess conftest.$ac_ext, and return whether this succeeded.
@@ -3938,51 +3892,6 @@ if test "x$enable_lts" = "xyes"; then :
 
 fi
 
-
-
-
-# checking pthread library
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for main in -lpthread" >&5
-$as_echo_n "checking for main in -lpthread... " >&6; }
-if ${ac_cv_lib_pthread_main+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-  ac_check_lib_save_LIBS=$LIBS
-LIBS="-lpthread  $LIBS"
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-
-int
-main ()
-{
-return main ();
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_link "$LINENO"; then :
-  ac_cv_lib_pthread_main=yes
-else
-  ac_cv_lib_pthread_main=no
-fi
-rm -f core conftest.err conftest.$ac_objext \
-    conftest$ac_exeext conftest.$ac_ext
-LIBS=$ac_check_lib_save_LIBS
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_pthread_main" >&5
-$as_echo "$ac_cv_lib_pthread_main" >&6; }
-if test "x$ac_cv_lib_pthread_main" = xyes; then :
-  cat >>confdefs.h <<_ACEOF
-#define HAVE_LIBPTHREAD 1
-_ACEOF
-
-  LIBS="-lpthread $LIBS"
-
-else
-  as_fn_error $? "*** POSIX thread support not installed ***" "$LINENO" 5
-fi
-
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
@@ -4380,14 +4289,6 @@ fi
 done
 
 
-ac_fn_c_check_header_mongrel "$LINENO" "pthread.h" "ac_cv_header_pthread_h" "$ac_includes_default"
-if test "x$ac_cv_header_pthread_h" = xyes; then :
-
-else
-  as_fn_error $? "*** POSIX thread support not installed ***" "$LINENO" 5
-fi
-
-
 ac_fn_c_check_header_mongrel "$LINENO" "linux/seccomp.h" "ac_cv_header_linux_seccomp_h" "$ac_includes_default"
 if test "x$ac_cv_header_linux_seccomp_h" = xyes; then :
 
diff --git a/configure.ac b/configure.ac
index fc5823143..5ef97cbd0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -291,12 +291,6 @@ AS_IF([test "x$enable_lts" = "xyes"], [
         AC_SUBST(HAVE_CONTRIB_INSTALL)
 ])
 
-
-
-
-# checking pthread library
-AC_CHECK_LIB([pthread], [main], [], AC_MSG_ERROR([*** POSIX thread support not installed ***]))
-AC_CHECK_HEADER(pthread.h,,AC_MSG_ERROR([*** POSIX thread support not installed ***]))
 AC_CHECK_HEADER([linux/seccomp.h],,AC_MSG_ERROR([*** SECCOMP support is not installed (/usr/include/linux/seccomp.h missing) ***]))
 
 # set sysconfdir
diff --git a/src/common.mk.in b/src/common.mk.in
index d117433dc..c8329e7c2 100644
--- a/src/common.mk.in
+++ b/src/common.mk.in
@@ -44,7 +44,7 @@ CFLAGS += -DPREFIX='"$(prefix)"' -DSYSCONFDIR='"$(sysconfdir)/firejail"' -DLIBDI
 MANFLAGS = $(HAVE_LTS) $(HAVE_OUTPUT) $(HAVE_X11) $(HAVE_PRIVATE_HOME) $(HAVE_APPARMOR) $(HAVE_OVERLAYFS) $(HAVE_USERTMPFS) $(HAVE_DBUSPROXY) $(HAVE_FIRETUNNEL) $(HAVE_GLOBALCFG) $(HAVE_CHROOT) $(HAVE_NETWORK) $(HAVE_USERNS) $(HAVE_FILE_TRANSFER) $(HAVE_SELINUX) $(HAVE_SUID) $(HAVE_FORCE_NONEWPRIVS)
 CFLAGS += $(MANFLAGS)
 CFLAGS += -fstack-protector-all -D_FORTIFY_SOURCE=2 -fPIE -Wformat -Wformat-security
-LDFLAGS += -pie -fPIE -Wl,-z,relro -Wl,-z,now -lpthread
+LDFLAGS += -pie -fPIE -Wl,-z,relro -Wl,-z,now
 EXTRA_LDFLAGS +=@EXTRA_LDFLAGS@
 
 ifdef NO_EXTRA_CFLAGS