Re-allow -fPIC compiler flag during compilation

We were temporally disabling this flag due to issues with PIC code
in static linking.  These issues should not be resolved.

Fixes: #9013

Author: sbc100

emcc.py

@@ -1883,9 +1883,6 @@ def is_link_flag(flag):
         return any(flag.startswith(x) for x in ('-l', '-L', '-Wl,'))
 
       compile_args = [a for a in newargs if a and not is_link_flag(a)]
-      if '-fPIC' in compile_args and not shared.Settings.RELOCATABLE:
-        shared.warning('ignoring -fPIC flag when not building with SIDE_MODULE or MAIN_MODULE')
-        compile_args.remove('-fPIC')
 
       # Bitcode args generation code
       def get_clang_command(input_files):

emscripten.py

@@ -2413,6 +2413,9 @@ def create_asm_consts_wasm(forwarded_json, metadata):
                      str(int(sync_proxy)) +
                      ', code, sigPtr, argbuf); }')
 
+    if shared.Settings.RELOCATABLE:
+      preamble += '\n  code -= %s;\n' % shared.Settings.GLOBAL_BASE
+
     asm_const_funcs.append(r'''
 function %s(code, sigPtr, argbuf) {%s
   var args = readAsmConstArgs(sigPtr, argbuf);

tests/test_core.py

@@ -8361,7 +8361,6 @@ def test_undefined_main(self):
 
   def test_fpic_static(self):
     self.emcc_args.append('-fPIC')
-    self.emcc_args.remove('-Werror')
     self.do_run_in_out_file_test('tests', 'core', 'test_hello_world')