Don't compute function tables at compile time with clang

The current code fails to compile with clang compilers on Linux and macOS.

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

Author: stweil

src/lstm/functions.cpp

@@ -20,7 +20,7 @@
 
 namespace tesseract {
 
-#if __cplusplus < 201402 // C++11
+#if __cplusplus < 201402 || defined(__clang__) // C++11
 
 double TanhTable[kTableSize];
 double LogisticTable[kTableSize];

src/lstm/functions.h

@@ -35,7 +35,7 @@ constexpr int kTableSize = 4096;
 // Scale factor for float arg to int index.
 constexpr double kScaleFactor = 256.0;
 
-#if __cplusplus < 201402 // C++11
+#if __cplusplus < 201402 || defined(__clang__) // C++11
 
 extern double TanhTable[];
 extern double LogisticTable[];