Fix build with clang 13 (dotnet#60328)

* Fix build with clang 13
Tested with:
```sh
$ clang --version | head -1
Ubuntu clang version 13.0.0-++20211006103153+fd1d8c2f04dd-1~exp1~20211006223759.3
```

* Fix gcc build

* Unify supressions

* Fix Clang 13 -Wcast-function-type warning

`cast from 'void (*)(int, siginfo_t *, void *)' to 'void (*)(int)' converts to incompatible function type`

But going through an intermediate `void (*) (void)` function type is allowed.

Co-authored-by: Aleksey Kliger <aleksey@lambdageek.org>

Author: am11

eng/native/configurecompiler.cmake

@@ -367,6 +367,8 @@ if (CLR_CMAKE_HOST_UNIX)
   #These seem to indicate real issues
   add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-Wno-invalid-offsetof>)
 
+  add_compile_options(-Wno-unused-but-set-variable)
+
   if (CMAKE_C_COMPILER_ID MATCHES "Clang")
     add_compile_options(-Wno-unknown-warning-option)
 
@@ -376,8 +378,6 @@ if (CLR_CMAKE_HOST_UNIX)
 
     # Disabled warnings
     add_compile_options(-Wno-unused-private-field)
-    # Explicit constructor calls are not supported by clang (this->ClassName::ClassName())
-    add_compile_options(-Wno-microsoft)
     # There are constants of type BOOL used in a condition. But BOOL is defined as int
     # and so the compiler thinks that there is a mistake.
     add_compile_options(-Wno-constant-logical-operand)
@@ -390,8 +390,9 @@ if (CLR_CMAKE_HOST_UNIX)
     # to a struct or a class that has virtual members or a base class. In that case, clang
     # may not generate the same object layout as MSVC.
     add_compile_options(-Wno-incompatible-ms-struct)
+
+    add_compile_options(-Wno-reserved-identifier)
   else()
-    add_compile_options(-Wno-unused-but-set-variable)
     add_compile_options(-Wno-uninitialized)
     add_compile_options(-Wno-strict-aliasing)
     add_compile_options(-Wno-array-bounds)

src/libraries/Native/Unix/System.Native/pal_process.c

@@ -191,6 +191,24 @@ static int SetGroups(uint32_t* userGroups, int32_t userGroupsLength, uint32_t* p
     return rv;
 }
 
+typedef void (*VoidIntFn)(int);
+
+static
+VoidIntFn
+handler_from_sigaction (struct sigaction *sa)
+{
+    if (((unsigned int)sa->sa_flags) & SA_SIGINFO)
+    {
+        // work around -Wcast-function-type
+        void (*tmp)(void) = (void (*)(void))sa->sa_sigaction;
+        return (void (*)(int))tmp;
+    }
+    else
+    {
+        return sa->sa_handler;
+    }
+}
+
 int32_t SystemNative_ForkAndExecProcess(const char* filename,
                                       char* const argv[],
                                       char* const envp[],
@@ -371,7 +389,7 @@ int32_t SystemNative_ForkAndExecProcess(const char* filename,
             }
             if (!sigaction(sig, NULL, &sa_old))
             {
-                void (*oldhandler)(int) = (((unsigned int)sa_old.sa_flags) & SA_SIGINFO) ? (void (*)(int))sa_old.sa_sigaction : sa_old.sa_handler;
+                void (*oldhandler)(int) = handler_from_sigaction (&sa_old);
                 if (oldhandler != SIG_IGN && oldhandler != SIG_DFL)
                 {
                     // It has a custom handler, put the default handler back.