cmake.bbclass: restore OECMAKE_SOURCEPATH

Some packages put their CMakeLists.txt file in a subdirectory, so assuming that
it is in ${S} won't work.

Restore OECMAKE_SOURCEPATH (defaulting to ${S}) so that the location of
CMakeLists.txt can be set if required.

Based on a patch by Miroslav Keš <miroslav.kes@gmail.com>

(From OE-Core rev: 2c23d7ab913a636aa0ab6a6e899cf6211d1e2714)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/cmake.bbclass

@@ -1,3 +1,6 @@
+# Path to the CMake file to process.
+OECMAKE_SOURCEPATH ?= "${S}"
+
 DEPENDS_prepend = "cmake-native "
 B = "${WORKDIR}/build"
 
@@ -65,8 +68,8 @@ EOF
 addtask generate_toolchain_file after do_patch before do_configure
 
 cmake_do_configure() {
-	if [ "${OECMAKE_BUILDPATH}" -o "${OECMAKE_SOURCEPATH}" ]; then
-		bbnote "cmake.bbclass no longer uses OECMAKE_SOURCEPATH and OECMAKE_BUILDPATH.  The default behaviour is now out-of-tree builds with B=WORKDIR/build."
+	if [ "${OECMAKE_BUILDPATH}" ]; then
+		bbnote "cmake.bbclass no longer uses OECMAKE_BUILDPATH.  The default behaviour is now out-of-tree builds with B=WORKDIR/build."
 	fi
 
 	if [ "${S}" != "${B}" ]; then
@@ -84,7 +87,7 @@ cmake_do_configure() {
 
 	cmake \
 	  ${OECMAKE_SITEFILE} \
-	  ${S} \
+	  ${OECMAKE_SOURCEPATH} \
 	  -DCMAKE_INSTALL_PREFIX:PATH=${prefix} \
 	  -DCMAKE_INSTALL_BINDIR:PATH=${bindir} \
 	  -DCMAKE_INSTALL_SBINDIR:PATH=${sbindir} \