[lld][WebAssembly] Fix non-pie dynamic-linking executable (#108146)

The commit 22b7b84
made the symbols provided by shared libraries "defined",
and thus effectively made it impossible to generate non-pie
dynamically linked executables using
--unresolved-symbols=import-dynamic.

This commit, based on #109249,
fixes it by checking sym->isShared() explictly.
(as a bonus, you don't need to rely on
--unresolved-symbols=import-dynamic
anymore.)

Fixes #107387

Author: yamt

lld/test/wasm/dylink-non-pie.s

@@ -0,0 +1,38 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.lib.o %p/Inputs/ret32.s
+# RUN: wasm-ld -m wasm32 --experimental-pic -shared --no-entry %t.lib.o -o %t.lib.so
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
+# RUN: wasm-ld -m wasm32 -Bdynamic %t.o %t.lib.so -o %t.wasm
+# RUN: obj2yaml %t.wasm | FileCheck %s
+# RUN: llvm-objdump -d --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DIS
+
+	.functype	ret32 (f32) -> (i32)
+	.globl	_start
+_start:
+	.functype	_start () -> ()
+	i32.const   f_p
+	drop
+	end_function
+
+	.section	.data.f_p,"",@
+f_p:
+	.int32	ret32
+	.size	f_p, 4
+
+# CHECK:      Sections:
+# CHECK-NEXT:   - Type:            CUSTOM
+# CHECK-NEXT:     Name:            dylink.0
+
+# non-pie executable doesn't import __memory_base
+# CHECK:   - Type:            IMPORT
+# CHECK-NOT: Field:           __memory_base
+
+# CHECK:   - Type:            EXPORT
+# CHECK:       - Name:            __wasm_apply_data_relocs
+# CHECK-NEXT:         Kind:            FUNCTION
+
+# DIS:    <__wasm_apply_data_relocs>:
+# DIS-EMPTY:
+# DIS-NEXT:    i32.const       1024
+# DIS-NEXT:    global.get      0
+# DIS-NEXT:    i32.store       0
+# DIS-NEXT:    end

lld/wasm/Relocations.cpp

@@ -144,7 +144,7 @@ void scanRelocations(InputChunk *chunk) {
       break;
     }
 
-    if (ctx.isPic ||
+    if (ctx.isPic || sym->isShared() ||
         (sym->isUndefined() &&
          ctx.arg.unresolvedSymbols == UnresolvedPolicy::ImportDynamic)) {
       switch (reloc.Type) {