Activate regression tests previously KNOWNBUG

These tests can now be executed in our test suite.

Author: romainbrenguier

regression/cbmc-concurrency/norace_array1/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG pthread
+CORE pthread
 main.c
 
 ^EXIT=0$

regression/cbmc-concurrency/norace_array2/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG pthread
+CORE pthread
 main.c
 
 ^EXIT=0$

regression/cbmc-concurrency/struct_and_array1/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE pthread
 main.c
 
 ^EXIT=0$