Add option to explicitly avoid using execinfo for backtraces

backtrace(3) from libexecinfo in musl will run into crash [1].

Provide an option to disable it explicitly even if libexecinfo is
present.

1: https://www.openwall.com/lists/musl/2021/07/17/1

CMakeLists.txt

@@ -361,6 +361,9 @@ macro (CMAKE_BUILD_UTILITIES)
   if(CMake_NO_CXX_STANDARD)
     set(KWSYS_CXX_STANDARD "")
   endif()
+  if(CMake_NO_SELF_BACKTRACE)
+    set(KWSYS_NO_EXECINFO 1)
+  endif()
   if(WIN32)
     # FIXME: Teach KWSys to hard-code these checks on Windows.
     set(KWSYS_C_HAS_CLOCK_GETTIME_MONOTONIC_COMPILED 0)