Fix integer overflow in multithreading threshold calculation for SYMM/SYRK (#4116)

* Fix potential integer overflow

interface/symm.c

@@ -166,7 +166,7 @@ void NAME(char *SIDE, char *UPLO,
   int nodes;
 #endif
 # if defined(SMP)
-  int MN;
+  double MN;
 #endif
   blasint info;
   int side;
@@ -264,7 +264,7 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_SIDE Side, enum CBLAS_UPLO Uplo,
   int nodes;
 #endif
 #if defined(SMP)
-  int MN;
+  double MN;
 #endif
 
   PRINT_DEBUG_CNAME;

interface/syrk.c

@@ -107,7 +107,7 @@ void NAME(char *UPLO, char *TRANS,
   FLOAT *sa, *sb;
 
 #ifdef SMP
-  int NNK;
+  double NNK;
 #ifdef USE_SIMPLE_THREADED_LEVEL3
 #ifndef COMPLEX
 #ifdef XDOUBLE
@@ -232,7 +232,7 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, enum CBLAS_TRANSPOSE Tr
   FLOAT *sa, *sb;
 
 #ifdef SMP
-int NNK;
+double NNK;
 
 #ifdef USE_SIMPLE_THREADED_LEVEL3
 #ifndef COMPLEX