Link libexecinfo if its found, this is needed for musl based systems

Fixes
ld: libglog.so.0.4.0: undefined reference to `backtrace'
| collect2: error: ld returned 1 exit status

Upstream-Status: Pending
Signed-off-by: Khem Raj <raj.khem@gmail.com>
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -144,6 +144,7 @@ check_cxx_compiler_flag (-Wunnamed-type-
 check_symbol_exists (snprintf cstdio HAVE_SNPRINTF)
 
 check_library_exists (dbghelp UnDecorateSymbolName "" HAVE_DBGHELP)
+check_library_exists (execinfo backtrace "" HAVE_EXECINFO)
 
 check_cxx_source_compiles ("
 #include <cstdlib>
@@ -584,6 +585,10 @@ if (Unwind_FOUND)
   set (Unwind_DEPENDENCY "find_dependency (Unwind ${Unwind_VERSION})")
 endif (Unwind_FOUND)
 
+if (HAVE_EXECINFO)
+  target_link_libraries (glog PUBLIC execinfo)
+endif (HAVE_EXECINFO)
+
 if (HAVE_DBGHELP)
    target_link_libraries (glog PUBLIC dbghelp)
 endif (HAVE_DBGHELP)