Link with -ldl option only when it is supported

-ldl option was used unconditionally while libdl is not supported
when libc is static.
Add build test to configure which checks if libdl is supported.
QMAKE_LIBS_DYNLOAD in "src/corelib/plugin/plugin.pri" is now used only
if libdl is available.
qt_linux_find_symbol_sys from qlibrary_unix is now used only if
QT_NO_DYNAMIC_LIBRARY is not defined.

Initially reported by Buildroot autobuilder here:
http://autobuild.buildroot.net/results/a85/a85a1839a45fb6102e53131ecc8f6dadf92bcdc2

Change-Id: I0397472456efdc4f3ab5f24d01253bee8048a9d1
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/configure b/configure
index 0c579b3e74..1473a62c5b 100755
--- a/configure
+++ b/configure
@@ -4734,6 +4734,12 @@ if [ "$CFG_LIBPNG" = "auto" ]; then
     fi
 fi
 
+# detect dl
+if ! compileTest unix/libdl "libdl"; then
+    QMakeVar add DEFINES QT_NO_DYNAMIC_LIBRARY
+    QMAKE_CONFIG="$QMAKE_CONFIG no-libdl"
+fi
+
 if [ "$CFG_EGLFS" = "yes" ]; then
     if [ "$CFG_EGL" = "no" ]; then
         echo "The EGLFS plugin requires EGL support and cannot be built"