cmake: do not install hook on throw when building tests

This fixes build of tests with STATIC=ON, which failed with:

/tmp/cc8lNtqY.ltrans12.ltrans.o: In function
`boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::thread_resource_error>
>::rethrow() const [clone .lto_priv.41]':
cc8lNtqY.ltrans12.o:(.text+0x4e): undefined reference to `__wrap___cxa_throw'

The hook is implemented in libcommon, which is not linked into some of the test
binaries.  An alternative solution is to link all tests against libcommon,
but that seems worse because it introduces a false dependency (also,
I tried that and for some of the test binaries the linker still failed to
pick up the symol from libcommon, strangely.)

CMakeLists.txt

@@ -295,7 +295,7 @@ link_directories(${LIBUNWIND_LIBRARY_DIRS})
 if(MSVC)
   add_definitions("/bigobj /MP /W3 /GS- /D_CRT_SECURE_NO_WARNINGS /wd4996 /wd4345 /D_WIN32_WINNT=0x0600 /DWIN32_LEAN_AND_MEAN /DGTEST_HAS_TR1_TUPLE=0 /FIinline_c.h /D__SSE4_1__")
   # set(COMMON_C_FLAGS "${COMMON_C_FLAGS} /Dinline=__inline")
-  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /STACK:10485760")
+  set(COMMON_EXE_LINKER_FLAGS "${COMMON_EXE_LINKER_FLAGS} /STACK:10485760")
   if(STATIC)
     foreach(VAR CMAKE_C_FLAGS_DEBUG CMAKE_CXX_FLAGS_DEBUG CMAKE_C_FLAGS_RELEASE CMAKE_CXX_FLAGS_RELEASE)
       string(REPLACE "/MD" "/MT" ${VAR} "${${VAR}}")
@@ -333,7 +333,7 @@ else()
     include_directories(SYSTEM src/platform/mingw)
     # mingw doesn't support LTO (multiple definition errors at link time)
     set(USE_LTO_DEFAULT false)
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--stack,10485760")
+    set(COMMON_EXE_LINKER_FLAGS "${COMMON_EXE_LINKER_FLAGS} -Wl,--stack,10485760")
     if(NOT BUILD_64)
       add_definitions(-DWINVER=0x0501 -D_WIN32_WINNT=0x0501)
     endif()
@@ -420,9 +420,11 @@ else()
   set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${DEBUG_FLAGS}")
   set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} ${RELEASE_FLAGS}")
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${RELEASE_FLAGS}")
+
   if(STATIC AND NOT APPLE AND NOT FREEBSD AND NOT OPENBSD)
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static-libgcc -static-libstdc++")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--wrap=__cxa_throw")
+    set(COMMON_EXE_LINKER_FLAGS "${COMMON_EXE_LINKER_FLAGS} -static-libgcc -static-libstdc++")
+    # Install hook on throw for dumping stack on exception (implemented in libcommon)
+    set(WRAP_CXA_THROW_FLAG "-Wl,--wrap=__cxa_throw")
   endif()
 endif()
 
@@ -471,9 +473,12 @@ endif()
 
 include(version.cmake)
 
-# When building the following sources, treat warnings as errors
+# When building the following sources...
+#   ...treat warnings as errors, install throw wrapper
 set(CMAKE_C_FLAGS "${COMMON_C_FLAGS} ${WARNINGS_AS_ERRORS_FLAG}")
 set(CMAKE_CXX_FLAGS "${COMMON_CXX_FLAGS} ${WARNINGS_AS_ERRORS_FLAG}")
+#   ...install hook on throw
+set(CMAKE_EXE_LINKER_FLAGS "${COMMON_EXE_LINKER_FLAGS} ${WRAP_CXA_THROW_FLAG}")
 
 add_subdirectory(contrib)
 add_subdirectory(src)
@@ -482,9 +487,12 @@ add_subdirectory(src)
 option(BUILD_TESTS "Build tests." OFF)
 
 if(BUILD_TESTS)
-  # When building tests, do *not* treat warnings as errors
+  # When building tests...
+  #  ...do *not* treat warnings as errors
   set(CMAKE_C_FLAGS "${COMMON_C_FLAGS}")
   set(CMAKE_CXX_FLAGS "${COMMON_CXX_FLAGS}")
+  #  ...do *not* install hook on throw
+  set(CMAKE_EXE_LINKER_FLAGS "${COMMON_CXX_FLAGS}")
   add_subdirectory(tests)
 endif()