Makefile: -lpthread may still be necessary when libc has only pthread stubs

Without this patch, systems that provide stubs for pthread functions
in libc, but which still require libpthread for full the pthread
implementation are not detected correctly.

Also, some systems require -pthread in CFLAGS for each compilation
unit for a successful link of an mt binary, which is also addressed by
this patch.

Signed-off-by: Gary V. Vaughan <gary@thewrittenword.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -294,6 +294,7 @@ RPMBUILD = rpmbuild
 TCL_PATH = tclsh
 TCLTK_PATH = wish
 PTHREAD_LIBS = -lpthread
+PTHREAD_CFLAGS =
 
 export TCL_PATH TCLTK_PATH
 
@@ -898,6 +899,8 @@ ifeq ($(uname_S),AIX)
 	BASIC_CFLAGS += -D_LARGE_FILES
 	ifeq ($(shell expr "$(uname_V)" : '[1234]'),1)
 		NO_PTHREADS = YesPlease
+	else
+		PTHREAD_LIBS = -lpthread
 	endif
 endif
 ifeq ($(uname_S),GNU)
@@ -1349,6 +1352,7 @@ endif
 ifdef NO_PTHREADS
 	BASIC_CFLAGS += -DNO_PTHREADS
 else
+	BASIC_CFLAGS += $(PTHREAD_CFLAGS)
 	EXTLIBS += $(PTHREAD_LIBS)
 	LIB_OBJS += thread-utils.o
 endif

config.mak.in

@@ -57,4 +57,5 @@ NO_DEFLATE_BOUND=@NO_DEFLATE_BOUND@
 FREAD_READS_DIRECTORIES=@FREAD_READS_DIRECTORIES@
 SNPRINTF_RETURNS_BOGUS=@SNPRINTF_RETURNS_BOGUS@
 NO_PTHREADS=@NO_PTHREADS@
+PTHREAD_CFLAGS=@PTHREAD_CFLAGS@
 PTHREAD_LIBS=@PTHREAD_LIBS@

configure.ac

@@ -802,7 +802,11 @@ AC_DEFUN([PTHREADTEST_SRC], [
 int main(void)
 {
 	pthread_mutex_t test_mutex;
-	return (0);
+	int retcode = 0;
+	retcode |= pthread_mutex_init(&test_mutex,(void *)0);
+	retcode |= pthread_mutex_lock(&test_mutex);
+	retcode |= pthread_mutex_unlock(&test_mutex);
+	return retcode;
 }
 ])
 
@@ -819,7 +823,8 @@ if test -n "$USER_NOPTHREAD"; then
 # handle these separately since PTHREAD_CFLAGS could be '-lpthreads
 # -D_REENTRANT' or some such.
 elif test -z "$PTHREAD_CFLAGS"; then
-  for opt in -pthread -lpthread; do
+  threads_found=no
+  for opt in -mt -pthread -lpthread; do
      old_CFLAGS="$CFLAGS"
      CFLAGS="$opt $CFLAGS"
      AC_MSG_CHECKING([Checking for POSIX Threads with '$opt'])
@@ -827,11 +832,18 @@ elif test -z "$PTHREAD_CFLAGS"; then
 	[AC_MSG_RESULT([yes])
 		NO_PTHREADS=
 		PTHREAD_LIBS="$opt"
+		PTHREAD_CFLAGS="$opt"
+		threads_found=yes
 		break
 	],
 	[AC_MSG_RESULT([no])])
       CFLAGS="$old_CFLAGS"
   done
+  if test $threads_found != yes; then
+    AC_CHECK_LIB([pthread], [pthread_create],
+	[PTHREAD_LIBS="-lpthread"],
+	[NO_PTHREADS=UnfortunatelyYes])
+  fi
 else
   old_CFLAGS="$CFLAGS"
   CFLAGS="$PTHREAD_CFLAGS $CFLAGS"
@@ -848,6 +860,7 @@ fi
 
 CFLAGS="$old_CFLAGS"
 
+AC_SUBST(PTHREAD_CFLAGS)
 AC_SUBST(PTHREAD_LIBS)
 AC_SUBST(NO_PTHREADS)