PR #1689: Minor: Add missing quotes in CMake string view library definition

Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1689

Merge c755474cd03d3da0efa68ec0605b183d24bfd5d6 into 2f61aed1

Merging this change closes #1689

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1689 from rschu1ze:missing-quotes c755474cd03d3da0efa68ec0605b183d24bfd5d6
PiperOrigin-RevId: 641896976
Change-Id: Iaf565a13ad639543c2f1ba698aefd18f8f48bede

absl/strings/CMakeLists.txt

@@ -18,9 +18,9 @@ absl_cc_library(
   NAME
     string_view
   HDRS
-    string_view.h
+    "string_view.h"
   SRCS
-    string_view.cc
+    "string_view.cc"
   COPTS
     ${ABSL_DEFAULT_COPTS}
   DEPS