Disable use of Linux memory protection keys

V8's default thread-isolated allocator has a bug on x64 Linux.

It uses memory protection keys (see `man 7 pkeys`) to
write-protect JIT code memory but in a way that is currently
incompatible with how we use threads.

Specifically, pkey permissions are inherited by child threads.
Threads that are not descendants of the thread that allocates
the pkey default to "no permissions" for that pkey.

Concretely, if thread A creates the v8::Platform (and the pkey)
and write-protects memory, then later thread B tries to access
that memory, it segfaults due to the lack of permissions.

The fix on V8's side is conceptually easy - call
pkey_set(PKEY_DISABLE_WRITE) before accessing the memory,
to flip the permissions from "none" to "can read" - but
until it's actually fixed, disable thread-isolation.

Fixes: rubyjs/mini_racer#300
Refs: https://issues.chromium.org/issues/360909072

Author: bnoordhuis

libexec/extract-node

@@ -32,6 +32,7 @@ cd "${src}/node-v${version}"
 #patch -p1 < "${top}"/patch/gyp-libv8_monolith.patch
 #patch -p1 < "${top}"/patch/py2-icutrim.patch
 #patch -p1 < "${top}"/patch/py2-genv8constants.patch
+patch -p1 < "${top}"/patch/v8-disable-pkey.patch
 
 # TODO: the following still fails on py3 so the above one forcing py2 is needed
 # patch -p1 < ../../py3-genv8constants.patch

patch/v8-disable-pkey.patch

@@ -0,0 +1,17 @@
+diff --git a/deps/v8/src/base/build_config.h b/deps/v8/src/base/build_config.h
+index 9ed4c8f102..dfca698506 100644
+--- a/deps/v8/src/base/build_config.h
++++ b/deps/v8/src/base/build_config.h
+@@ -35,11 +35,8 @@
+ #define V8_HAS_PTHREAD_JIT_WRITE_PROTECT 0
+ #endif
+ 
+-#if defined(V8_OS_LINUX) && defined(V8_HOST_ARCH_X64)
+-#define V8_HAS_PKU_JIT_WRITE_PROTECT 1
+-#else
++// disabled, see https://issues.chromium.org/issues/360909072
+ #define V8_HAS_PKU_JIT_WRITE_PROTECT 0
+-#endif
+ 
+ #if defined(V8_TARGET_ARCH_IA32) || defined(V8_TARGET_ARCH_X64)
+ #define V8_TARGET_ARCH_STORES_RETURN_ADDRESS_ON_STACK true