Move big-int unit test to unit/ folder and make it a CATCH-style test

Author: tautschnig

.gitignore

@@ -109,8 +109,6 @@ src/goto-diff/goto-diff
 src/goto-diff/goto-diff.exe
 src/clobber/clobber
 src/clobber/clobber.exe
-src/big-int/test-bigint
-src/big-int/test-bigint.exe
 jbmc/src/janalyzer/janalyzer
 jbmc/src/janalyzer/janalyzer.exe
 jbmc/src/jdiff/jdiff

CMakeLists.txt

@@ -70,7 +70,6 @@ set_target_properties(
     linking
     pointer-analysis
     solvers
-    test-bigint
     testing-utils
     unit
     util

src/big-int/CMakeLists.txt

@@ -1,6 +1,5 @@
 set(SRC bigint-func.cc bigint.cc)
 
-add_executable(test-bigint ${SRC} bigint-test.cc)
 add_library(big-int ${SRC})
 
 generic_includes(big-int)