[libc] change ASAN condition to generator expression

[michaelrj]

Summary

Previously, building LLVM-libc with GWP ASAN was conditioned on the flag
COMPILER_RT_BUILD_GWP_ASAN, which caused issues do to the default value
of the flag being set in the compiler-rt cmake, which is seperate. Now
GWP ASAN is included based on if it exists as a target, which is more
consistent.

[sivachandra]

libc/src/stdlib/CMakeLists.txt

206

Using it in an if block does not seem to change the semantics. However, the following works for me:

list(APPEND SCUDO_DEPS $<$<TARGET_EXISTS:RTGwpAsan.${LIBC_TARGET_ARCHITECTURE}>:RTGwpAsan.${LIBC_TARGET_ARCHITECTURE}>
                       $<$<TARGET_EXISTS:RTGwpAsanBacktraceLibc.${LIBC_TARGET_ARCHITECTURE}>:RTGwpAsanBacktraceLibc.${LIBC_TARGET_ARCHITECTURE}>
                       $<$<TARGET_EXISTS:RTGwpAsanSegvHandler.${LIBC_TARGET_ARCHITECTURE}>:RTGwpAsanSegvHandler.${LIBC_TARGET_ARCHITECTURE}>)

[michaelrj]

switch to TARGET_NAME_IF_EXISTS

[michaelrj]

move the checking to inside the library rules

libc/src/stdlib/CMakeLists.txt

 if(LLVM_LIBC_INCLUDE_SCUDO)
   set(SCUDO_DEPS "")
 
   include(${LIBC_SOURCE_DIR}/../compiler-rt/cmake/Modules/AllSupportedArchDefs.cmake)
   if(NOT (LIBC_TARGET_ARCHITECTURE IN_LIST ALL_SCUDO_STANDALONE_SUPPORTED_ARCH))
     message(FATAL_ERROR "Architecture ${LIBC_TARGET_ARCHITECTURE} is not supported by SCUDO. 
       Either disable LLVM_LIBC_INCLUDE_SCUDO or change your target architecture.")
   endif()
-  list(APPEND SCUDO_DEPS RTScudoStandalone.${LIBC_TARGET_ARCHITECTURE} 
-       RTScudoStandaloneCWrappers.${LIBC_TARGET_ARCHITECTURE})
-  if((LIBC_TARGET_ARCHITECTURE IN_LIST ALL_GWP_ASAN_SUPPORTED_ARCH) 
-      AND COMPILER_RT_BUILD_GWP_ASAN)
+
+  list(APPEND SCUDO_DEPS RTScudoStandalone.${LIBC_TARGET_ARCHITECTURE}
+
+  if($<TARGET_EXISTS:RTGwpAsan.${LIBC_TARGET_ARCHITECTURE}>)
     list(APPEND SCUDO_DEPS RTGwpAsan.${LIBC_TARGET_ARCHITECTURE} 
                             RTGwpAsanBacktraceLibc.${LIBC_TARGET_ARCHITECTURE} 
                             RTGwpAsanSegvHandler.${LIBC_TARGET_ARCHITECTURE})
-  elseif(COMPILER_RT_BUILD_GWP_ASAN)
-    message(WARNING "Architecture ${LIBC_TARGET_ARCHITECTURE} is not supported by GWP-ASan. Skipping.")
   endif()
 
   add_entrypoint_external(
     malloc
     DEPENDS
       ${SCUDO_DEPS}
   )
   add_entrypoint_external(