V8: fix relocation error

```
ld.lld: error: relocation R_X86_64_TPOFF32 against v8::internal::g_current_local_heap_ cannot be used with -shared
ld.lld: error: relocation R_386_TLS_LE against v8::internal::g_current_isolate_ cannot be used with -shared
ld.lld: error: relocation R_ARM_TLS_LE32 against v8::internal::g_current_isolate_ cannot be used with -shared
ld.lld: error: relocation R_AARCH64_TLSLE_ADD_TPREL_HI12 against v8::internal::g_current_local_heap_ cannot be used with -shared
relocation R_X86_64_TPOFF32 against hidden symbol `_ZN2v88internal18g_current_isolate_E' can not be used when making a shared object
```

patches/linux/v8.patch

@@ -0,0 +1,12 @@
+diff --git a/BUILD.gn b/BUILD.gn
+index 6a4efbb03ee..9c0a45df4a5 100644
+--- a/BUILD.gn
++++ b/BUILD.gn
+@@ -1096,6 +1096,7 @@ config("features") {
+
+   defines =
+       [ "V8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=${v8_typed_array_max_size_in_heap}" ]
++  defines += ["V8_TLS_USED_IN_LIBRARY"]
+
+   configs = [
+     ":v8_header_features",

steps/03-patch.sh

@@ -22,6 +22,10 @@ case "$OS" in
     [ "${PDFium_ENABLE_V8:-}" == "true" ] && git -C v8 apply -v "$PATCHES/ios/v8.patch"
     ;;
 
+  linux)
+    [ "${PDFium_ENABLE_V8:-}" == "true" ] && git -C v8 apply -v "$PATCHES/linux/v8.patch"
+    ;;
+
   wasm)
     git apply -v "$PATCHES/wasm/pdfium.patch"
     git -C build apply -v "$PATCHES/wasm/build.patch"