Stop redefining static_assert for C++ cross-builds

CMakeLists.txt

@@ -806,12 +806,11 @@ else()
     set(STATIC_ASSERT_FLAG "-Dstatic_assert=_Static_assert")
   endif()
 
-  try_compile(STATIC_ASSERT_CPP_RES "${CMAKE_CURRENT_BINARY_DIR}/static-assert" "${CMAKE_CURRENT_SOURCE_DIR}/cmake/test-static-assert.cpp" CMAKE_FLAGS -DCMAKE_CXX_STANDARD=11)
-  if(STATIC_ASSERT_CPP_RES)
-    set(STATIC_ASSERT_CPP_FLAG "")
-  else()
-    set(STATIC_ASSERT_CPP_FLAG "-Dstatic_assert=_Static_assert")
-  endif()
+  # Cross try_compile has been observed to incorrectly fail for some C++ toolchains
+  # even though the compiler fully supports C++11 static_assert. Remapping
+  # static_assert breaks modern libstdc++/Boost headers, so keep the C fallback
+  # only and never redefine static_assert for C++.
+  set(STATIC_ASSERT_CPP_FLAG "")
 
   monero_enable_coverage()
   # With GCC 6.1.1 the compiled binary malfunctions due to aliasing. Until that