CMakeLists.txt (FT_ENABLE_ERROR_STRINGS): New configuration option.

This option uncomments FreeType configuration macro
`FT_CONFIG_OPTION_ERROR_STRINGS` to make function `FT_Error_String` return
meaningful error strings.

This option is off by default.

CMakeLists.txt

@@ -61,6 +61,8 @@
 #
 # Some notes.
 #
+# - Say `cmake -LAH` to see all configuration options.
+#
 # - `cmake' creates configuration files in
 #
 #     <build-directory>/include/freetype/config
@@ -215,6 +217,8 @@ cmake_dependent_option(FT_REQUIRE_BROTLI
   "Require support of compressed WOFF2 fonts." OFF
   "NOT FT_DISABLE_BROTLI" OFF)
 
+option(FT_ENABLE_ERROR_STRINGS
+  "Enable support for meaningful error descriptions." OFF)
 
 # Disallow in-source builds
 if ("${CMAKE_BINARY_DIR}" STREQUAL "${CMAKE_SOURCE_DIR}")
@@ -354,6 +358,12 @@ if (BROTLIDEC_FOUND)
     FTOPTION_H "${FTOPTION_H}")
 endif ()
 
+if (FT_ENABLE_ERROR_STRINGS)
+  string(REGEX REPLACE
+    "/\\* +(#define +FT_CONFIG_OPTION_ERROR_STRINGS) +\\*/" "\\1"
+    FTOPTION_H "${FTOPTION_H}")
+endif ()
+
 set(FTOPTION_H_NAME "${PROJECT_BINARY_DIR}/include/freetype/config/ftoption.h")
 if (EXISTS "${FTOPTION_H_NAME}")
   file(READ "${FTOPTION_H_NAME}" ORIGINAL_FTOPTION_H)