imgui_freetype: fixed non-ASCII characters in sources. (#6166)

misc/freetype/imgui_freetype.cpp

@@ -52,7 +52,7 @@
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wpragmas"                  // warning: unknown option after '#pragma GCC diagnostic' kind
 #pragma GCC diagnostic ignored "-Wunused-function"          // warning: 'xxxx' defined but not used
-#pragma GCC diagnostic ignored "-Wsubobject-linkage"        // warning: 'xxxx' has a field ‘xxxx’ whose type uses the anonymous namespace
+#pragma GCC diagnostic ignored "-Wsubobject-linkage"        // warning: 'xxxx' has a field 'xxxx' whose type uses the anonymous namespace
 #endif
 
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