[libcxx][libcxxabi][libunwind] Use libgcc on Android

Android doesn't have a libgcc_s and uses libgcc instead, so adjust the
build accordingly. This matches compiler-rt's build setup. libc++abi and
libunwind were already checking for libgcc but in a different context.
This change makes them search only for libgcc on Android now, but the
code to link against libgcc if it were present was already there.

Reviewed By: #libc, #libc_abi, #libunwind, rprichard, srhines

Differential Revision: https://reviews.llvm.org/D78787

Author: smeenai

libcxx/CMakeLists.txt

@@ -757,6 +757,8 @@ function(cxx_link_system_libraries target)
     if (LIBCXX_BUILTINS_LIBRARY)
       target_link_libraries(${target} PRIVATE "${LIBCXX_BUILTINS_LIBRARY}")
     endif()
+  elseif (LIBCXX_HAS_GCC_LIB)
+    target_link_libraries(${target} PRIVATE gcc)
   elseif (LIBCXX_HAS_GCC_S_LIB)
     target_link_libraries(${target} PRIVATE gcc_s)
   endif()

libcxx/cmake/config-ix.cmake

@@ -16,7 +16,11 @@ if (NOT LIBCXX_USE_COMPILER_RT)
   if(WIN32 AND NOT MINGW)
     set(LIBCXX_HAS_GCC_S_LIB NO)
   else()
-    check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXX_HAS_GCC_S_LIB)
+    if(ANDROID)
+      check_library_exists(gcc __gcc_personality_v0 "" LIBCXX_HAS_GCC_LIB)
+    else()
+      check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXX_HAS_GCC_S_LIB)
+    endif()
   endif()
 endif()
 
@@ -37,6 +41,8 @@ if (LIBCXX_SUPPORTS_NODEFAULTLIBS_FLAG)
     list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
     find_compiler_rt_library(builtins LIBCXX_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBCXX_BUILTINS_LIBRARY}")
+  elseif (LIBCXX_HAS_GCC_LIB)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES gcc)
   elseif (LIBCXX_HAS_GCC_S_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
   endif ()

libcxxabi/cmake/config-ix.cmake

@@ -6,8 +6,12 @@ include(CheckCSourceCompiles)
 
 check_library_exists(c fopen "" LIBCXXABI_HAS_C_LIB)
 if (NOT LIBCXXABI_USE_COMPILER_RT)
-  check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_S_LIB)
-  check_library_exists(gcc __aeabi_uldivmod "" LIBCXXABI_HAS_GCC_LIB)
+  if (ANDROID)
+    check_library_exists(gcc __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_LIB)
+  else ()
+    check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_S_LIB)
+    check_library_exists(gcc __aeabi_uldivmod "" LIBCXXABI_HAS_GCC_LIB)
+  endif ()
 endif ()
 
 # libc++abi is built with -nodefaultlibs, so we want all our checks to also

libunwind/cmake/config-ix.cmake

@@ -8,8 +8,12 @@ include(CheckCSourceCompiles)
 check_library_exists(c fopen "" LIBUNWIND_HAS_C_LIB)
 
 if (NOT LIBUNWIND_USE_COMPILER_RT)
-  check_library_exists(gcc_s __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_S_LIB)
-  check_library_exists(gcc __absvdi2 "" LIBUNWIND_HAS_GCC_LIB)
+  if (ANDROID)
+    check_library_exists(gcc __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_LIB)
+  else ()
+    check_library_exists(gcc_s __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_S_LIB)
+    check_library_exists(gcc __absvdi2 "" LIBUNWIND_HAS_GCC_LIB)
+  endif ()
 endif()
 
 # libunwind is built with -nodefaultlibs, so we want all our checks to also