[libc] Replace -nostdlib++ flag when building with gcc and add placement new operator to HermeticTestUtils.cpp. (#78906)

`-nostdlib++` is a clang-only flag. Replacing it with `-nostdlib` when
building with gcc.

Author: lntue

libc/cmake/modules/CheckCompilerFeatures.cmake

@@ -62,3 +62,6 @@ message(STATUS "Compiler features available: ${AVAILABLE_COMPILER_FEATURES}")
 
 # clang-8+, gcc-12+
 check_cxx_compiler_flag("-ftrivial-auto-var-init=pattern" LIBC_CC_SUPPORTS_PATTERN_INIT)
+
+# clang-6+, gcc-13+
+check_cxx_compiler_flag("-nostdlib++" LIBC_CC_SUPPORTS_NOSTDLIBPP)

libc/cmake/modules/LLVMLibCTestRules.cmake

@@ -435,6 +435,13 @@ function(add_libc_fuzzer target_name)
 
 endfunction(add_libc_fuzzer)
 
+# Get libgcc_s to be used in hermetic and integration tests.
+if(NOT LIBC_CC_SUPPORTS_NOSTDLIBPP)
+  execute_process(COMMAND ${CMAKE_CXX_COMPILER} -print-file-name=libgcc_s.so.1
+                  OUTPUT_VARIABLE LIBGCC_S_LOCATION)
+  string(STRIP ${LIBGCC_S_LOCATION} LIBGCC_S_LOCATION)
+endif()
+
 # DEPRECATED: Use add_hermetic_test instead.
 #
 # Rule to add an integration test. An integration test is like a unit test
@@ -564,8 +571,13 @@ function(add_integration_test test_name)
 
   if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
     target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
-  else()
+  elseif(LIBC_CC_SUPPORTS_NOSTDLIBPP)
     target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib++ -static)
+  else()
+    # Older version of gcc does not support `nostdlib++` flag.  We use
+    # `nostdlib` and link against libgcc_s, which cannot be linked statically.
+    target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib)
+    list(APPEND link_libraries ${LIBGCC_S_LOCATION})
   endif()
   target_link_libraries(
     ${fq_build_target_name}
@@ -741,8 +753,13 @@ function(add_libc_hermetic_test test_name)
 
   if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
     target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
-  else()
+  elseif(LIBC_CC_SUPPORTS_NOSTDLIBPP)
     target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib++ -static)
+  else()
+    # Older version of gcc does not support `nostdlib++` flag.  We use
+    # `nostdlib` and link against libgcc_s, which cannot be linked statically.
+    target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib)
+    list(APPEND link_libraries ${LIBGCC_S_LOCATION})
   endif()
   target_link_libraries(
     ${fq_build_target_name}

libc/test/UnitTest/HermeticTestUtils.cpp

@@ -104,6 +104,8 @@ void *__dso_handle = nullptr;
 
 } // extern "C"
 
+void *operator new(unsigned long size, void *ptr) { return ptr; }
+
 void *operator new(size_t size) { return malloc(size); }
 
 void *operator new[](size_t size) { return malloc(size); }
@@ -113,3 +115,5 @@ void operator delete(void *) {
   // we just trap here to catch any such accidental usages.
   __builtin_trap();
 }
+
+void operator delete(void *ptr, size_t size) { __builtin_trap(); }