[libc] Fix pthread argument for scudo integration tests when using GCC

[DavidSpickett]

Summary

This adds "-pthreads" which appears to be a clang only
alias for "-pthread" (all the drivers check for both).

Use "-pthread" instead to be compatible with gcc.

Otherwise you get:
FAILED: bin/libc-gwp-asan-uaf-should-crash
: && /usr/bin/g++-11 <...> -pthreads <...> projects/libc/test/integration/scudo/liblibc_for_scudo_integration_test.a && :
g++-11: error: unrecognized command-line option ‘-pthreads’; did you mean ‘-pthread’?

[michaelrj]

LGTM

libc/test/integration/scudo/CMakeLists.txt

 add_executable(
   libc-scudo-integration-test
   integration_test.cpp
 )
 
 target_link_options(
   libc-scudo-integration-test
   PRIVATE
-  -pthreads
+  -pthread
 )
 
 target_link_libraries(libc-scudo-integration-test
   PRIVATE
   libc_for_scudo_integration_test
 )
 
 add_executable(
   libc-gwp-asan-uaf-should-crash
   gwp_asan_should_crash.cpp
 )
 
 target_link_options(
   libc-gwp-asan-uaf-should-crash
   PRIVATE
-  -pthreads
+  -pthread
 )
 
 target_link_libraries(libc-gwp-asan-uaf-should-crash
   PRIVATE
   libc_for_scudo_integration_test
 )
 
 add_custom_command(TARGET libc-scudo-integration-test
                    POST_BUILD
                    COMMAND $<TARGET_FILE:libc-scudo-integration-test>
                    COMMENT "Run the test after it is built." 
                    VERBATIM)