cmake: more syntax tidy-up

- quote string literals.
  In the hope it improves syntax-highlighting and readability.

- use lowercase, underscore-prefixed local var names.
  As a hint for scope, to help readability.

- prefer `pkg_search_module` (over `pkg_check_modules`).
  They are the same, but `pkg_search_module` stops searching
  at the first hit.

- more `IN LISTS` in `foreach()`.

- OtherTests.cmake: clear `CMAKE_EXTRA_INCLUDE_FILES` after use.

- add `PROJECT_LABEL` for http/client and unit test targets.

- sync `Find*` module comments and formatting.

- drop a few local variables.

- drop bogus `CARES_LIBRARIES` from comment.

- unquote numeric literal.

Follow-up to acbc6b703f #14197
Closes #14388

docs/examples/CMakeLists.txt

@@ -23,9 +23,8 @@
 ###########################################################################
 
 # Get 'check_PROGRAMS' variable
-transform_makefile_inc("Makefile.inc"
-  "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
-include(${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake)
+transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
+include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 
 foreach(_example IN LISTS check_PROGRAMS)
   set(_example_target "curl-example-${_example}")
@@ -35,5 +34,6 @@ foreach(_example IN LISTS check_PROGRAMS)
   if(LIB_SELECTED STREQUAL LIB_STATIC AND WIN32)
     set_property(TARGET ${_example_target} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_STATICLIB")
   endif()
-  set_target_properties(${_example_target} PROPERTIES OUTPUT_NAME "${_example}" UNITY_BUILD OFF)
+  set_target_properties(${_example_target} PROPERTIES
+    OUTPUT_NAME "${_example}" UNITY_BUILD OFF)
 endforeach()