Fix compiler errors for old gcc

Travis CI with gcc 4.8 failed with errors.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/ccutil/unicodes.cpp

@@ -20,9 +20,9 @@
 
 namespace tesseract {
 
-constexpr const char *kLRM = "\u200E";  // Left-to-Right Mark
-constexpr const char *kRLM = "\u200F";  // Right-to-Left Mark
-constexpr const char *kRLE = "\u202A";  // Right-to-Left Embedding
-constexpr const char *kPDF = "\u202C";  // Pop Directional Formatting
+const char * const kLRM = "\u200E";  // Left-to-Right Mark
+const char * const kRLM = "\u200F";  // Right-to-Left Mark
+const char * const kRLE = "\u202A";  // Right-to-Left Embedding
+const char * const kPDF = "\u202C";  // Pop Directional Formatting
 
 }  // namespace

src/classify/featdefs.cpp

@@ -29,10 +29,10 @@
 /*-----------------------------------------------------------------------------
         Global Data Definitions and Declarations
 -----------------------------------------------------------------------------*/
-constexpr const char* kMicroFeatureType = "mf";
-constexpr const char* kCNFeatureType = "cn";
-constexpr const char* kIntFeatureType = "if";
-constexpr const char* kGeoFeatureType = "tb";
+const char* const kMicroFeatureType = "mf";
+const char* const kCNFeatureType = "cn";
+const char* const kIntFeatureType = "if";
+const char* const kGeoFeatureType = "tb";
 
 // Define all of the parameters for the MicroFeature type.
 StartParamDesc(MicroFeatureParams)