[cmake] Make `FindHarfbuzz' observe the REQUIRED option.

* builds/cmake/FindHarfBuzz.cmake: Implement it.

ChangeLog

@@ -1,3 +1,9 @@
+2015-11-27  Tamas Kenez  <tamas.kenez@adasworks.com>
+
+	[cmake] Make `FindHarfbuzz' observe the REQUIRED option.
+
+	* builds/cmake/FindHarfBuzz.cmake: Implement it.
+
 2015-11-27  Werner Lemberg  <wl@gnu.org>
 
 	[cmake] Collect files specific to cmake in `builds/cmake'.

builds/cmake/FindHarfBuzz.cmake

@@ -44,15 +44,26 @@ find_library(HARFBUZZ_LIBRARIES NAMES harfbuzz
 
 # HarfBuzz 0.9.18 split ICU support into a separate harfbuzz-icu library.
 if ("${PC_HARFBUZZ_VERSION}" VERSION_GREATER "0.9.17")
-    pkg_check_modules(PC_HARFBUZZ_ICU harfbuzz-icu>=0.9.18 REQUIRED)
+    if (HarfBuzz_FIND_REQUIRED)
+        set(_HARFBUZZ_REQUIRED REQUIRED)
+    else ()
+        set(_HARFBUZZ_REQUIRED "")
+    endif ()
+    pkg_check_modules(PC_HARFBUZZ_ICU harfbuzz-icu>=0.9.18 ${_HARFBUZZ_REQUIRED})
     find_library(HARFBUZZ_ICU_LIBRARIES NAMES harfbuzz-icu
         HINTS ${PC_HARFBUZZ_ICU_LIBRARY_DIRS} ${PC_HARFBUZZ_ICU_LIBDIR}
     )
-    list(APPEND HARFBUZZ_LIBRARIES "${HARFBUZZ_ICU_LIBRARIES}")
+    if (HARFBUZZ_ICU_LIBRARIES)
+        list(APPEND HARFBUZZ_LIBRARIES "${HARFBUZZ_ICU_LIBRARIES}")
+    endif ()
+    set(_HARFBUZZ_EXTRA_REQUIRED_VAR "HARFBUZZ_ICU_LIBRARIES")
+else ()
+    set(_HARFBUZZ_EXTRA_REQUIRED_VAR "")
 endif ()
 
 include(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(HarfBuzz DEFAULT_MSG HARFBUZZ_INCLUDE_DIRS HARFBUZZ_LIBRARIES)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(HarfBuzz DEFAULT_MSG HARFBUZZ_INCLUDE_DIRS
+    HARFBUZZ_LIBRARIES ${_HARFBUZZ_EXTRA_REQUIRED_VAR})
 
 mark_as_advanced(
     HARFBUZZ_ICU_LIBRARIES