snappy: modify cmake variable to generate shared library

FILES_${PN}-xxx under packages-split/ depend on FILES_${PN}.
But the FILES_${PN} is empty. This is because snappy doesn't
generate shared library by default.

So we should modify cmake variable to generate shared library.

Signed-off-by: Hongzhi.Song <hongzhi.song@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-extended/snappy/snappy_1.1.7.bb

@@ -20,3 +20,6 @@ inherit cmake pkgconfig
 PACKAGECONFIG ??= ""
 PACKAGECONFIG[lzo] = "-DHAVE_LIBLZO2=1,-DHAVE_LIBLZO2=0,lzo,"
 TARGET_CFLAGS += "-fPIC"
+
+EXTRA_OECMAKE += '-DBUILD_SHARED_LIBS="ON" \
+                  '