version.cmake: filter git describe matches

only use those that start with v[0-9] to avoid picking up a newer tag
which may not match the expected vX.Y.Z format. this is the same
invocation used by libvpx.

Bug: aomedia:3177
Fixed: aomedia:3177
Change-Id: I7dbab56088b32d33442f8a40dae0f1fdd3e2dc88
(cherry picked from commit 785759347a5a9b0d3d0ac71ac0904c93ffbe36e0)

build/cmake/version.cmake

diff --git a/build/cmake/version.cmake b/build/cmake/version.cmake
index dd953a3..f4377a1 100644
--- a/build/cmake/version.cmake
+++ b/build/cmake/version.cmake
@@ -24,7 +24,9 @@
 # Generate the version string for this run.
 unset(aom_version)
 if(EXISTS "${GIT_EXECUTABLE}")
-  execute_process(COMMAND ${GIT_EXECUTABLE} --git-dir=${AOM_ROOT}/.git describe
+  execute_process(COMMAND ${GIT_EXECUTABLE}
+                          --git-dir=${AOM_ROOT}/.git describe
+                          --match=v[0-9]*
                   OUTPUT_VARIABLE aom_version
                   ERROR_QUIET
                   RESULT_VARIABLE version_check_result)