[libc++abi] Also build the static archive with C++17

The dylib and the static archive should really be built using the same
Standard, it was just an oversight.

GitOrigin-RevId: aae2ff645bd5d89e4618bcd6d1ee0f115f3d47d3
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 10300d1..85e3fda 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -234,7 +234,7 @@
                           CXX_EXTENSIONS
                             OFF
                           CXX_STANDARD
-                            11
+                            17
                           CXX_STANDARD_REQUIRED
                             ON
                           COMPILE_FLAGS