0031038: Draw - adaptations for running tests with CLang address sanitizer

New optional environment variable CSF_CPULIMIT_FACTOR is introduced, allowing scaling the argument given to DRAW command cpulimit by specified factor.

Command testgrid is extended by two new options:
- -skipped: to re-run tests skipped in specified log
- -skip: to skip specified number of tests in the beginning of test sequence

Temporary Tcl scripts generated by test system are now removed from the test log directories immediately after the test execution, to save disk space.

Advises on use of CLang sanitizers are added in guide "Debugging hints and tips".

dox/dev_guides/debug/debug.md

@@ -368,3 +368,53 @@ Each counter has its name shown when the collected statistics are printed.
 In DRAW, use command *dperf* to print all performance statistics.
 
 Note that performance counters are not thread-safe.
+
+@section occt_debug_sanitizers Use of compiler sanitizers
+
+GCC and Clang compilers provide options for instrumenting the code with the tools intended for detection of run-time errors, called sanitizers.
+This section provides some hints for using sanitizers for detecting possible errors in OCCT code.
+
+@subsection occt_debug_sanitizers_linux Linux
+
+Example of configuration steps for Ubuntu:
+
+1. In CMake configuration:
+
+  - Use up-to-date version of the GCC or CLang compiler; make sure that if CMAKE_CXX_COMPILER is set to C++ compiler (e.g. "clang++-6.0") and CMAKE_C_COMPILER is set to C compiler (e.g. "clang-6.0")
+  - Ensure that CMAKE_LINKER is set to the C++ linker bundled with compiler (e.g. clang++-6.0); this is important to avoid linking problems
+  - For building with Address sanitizer, set CMAKE_CXX_FLAGS and CMAKE_C_FLAGS to "-fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls"
+  - For building with Undefined Behavior sanitizer, set CMAKE_CXX_FLAGS and CMAKE_C_FLAGS to "-fsanitize=undefined -fno-omit-frame-pointer -fno-optimize-sibling-calls"
+  - Set CMAKE_BUILD_TYPE to RelWithDebInfo to get more informative stack traces on errors
+
+2. Build as usual (make)
+
+  Be prepared that it works much slower than normal build and consumes more disk space.
+
+3. Before running executable, make sure that "llvm-symbolizer" is in PATH; this is necessary to get human-readable stack traces. The tool must have exactly that name.
+
+  If it is installed in common folder (/usr/bin or similar) with different name, one option is to create a symlink, for instance:
+> sudo ln -s /usr/bin/llvm-symbolizer-6.0 /usr/bin/llvm-symbolizer
+
+  Alternatively, add directory where actual llvm-symbolizer is located (such as /usr/lib/llvm-6.0/bin) to the PATH variable. 
+
+4. Set environment variable to disable memory leaks detection (they seem to be reported for every global variable at exit, not much useful):
+> export ASAN_OPTIONS=detect_leaks=0
+
+5. Set environment variable CSF_CPULIMIT_FACTOR to reasonably large number to increase the time limits for program execution (used by OCCT tests) to compensate the performance penalty introduced by sanitizers:
+> export CSF_CPULIMIT_FACTOR=20
+
+6. When using UBSan, set environment variable UBSAN_OPTIONS to get stack traces:
+> export UBSAN_OPTIONS=print_stacktrace=1
+
+7. Run DRAW and perform tests as usual, keeping in mind that running with sanitizer is much heavier than normal build:
+> ./draw.sh relwithdeb  <br>
+> Draw[]> testgrid -parallel 0
+
+Note that when running tests under sanitizers, behavior may be different.
+Known problems (as of CLang 6.0) are:
+- Software signals (access violation etc.) are not handled
+- Heap memory usage always reports zero
+
+@subsection occt_debug_sanitizers_windows Windows
+
+Though CLang toolset is available in Visual Studio 2015 and newer, sanitizer do not seem to be available out of the box (last tested with VS 2019 16.2.3).