pcre2: Add JIT-support for select architectures in PCRE2

- This commit adds a config-option for JIT in libpcre2.

  According to research published on
  https://rust-leipzig.github.io/regex/2017/03/28/comparison-of-regex-engines/
  this should give a 10x performance increase on JIT operations
  which can be desireable for high performance Apache mod_rewrite
  or haproxy reqrep operations.

  This option is available on all officially supported architecutres
  which are listed on https://pcre.org/current/doc/html/pcre2jit.html#SEC2.
  Furthermore, it is enabled by default on the following
  architectures: arm, i686, x86_64.

Signed-off-by: Christian Lachner <gladiac@gmail.com>

libs/pcre2/Config.in

@@ -0,0 +1,30 @@
+config PCRE2_JIT_ENABLED
+	bool
+	depends on PACKAGE_libpcre2 && (aarch64 || aarch64_be || arm || i386 || i686 || x86_64 || mips || mipsel || mips64 || mips64el || powerpc || powerpc64 || powerpcle || sparc)
+	default y if (arm || i686 || x86_64)
+	prompt "Enable JIT compiler support"
+	help
+		Enable JIT (Just-In-Time) compiler support.
+
+		Just-in-time compiling is a heavyweight optimization that can greatly
+		speed up pattern matching. However, it comes at the cost of extra
+		processing before the match is performed, so it is of most benefit when
+		the same pattern is going to be matched many times. This does not
+		necessarily mean many calls of a matching function; if the pattern is
+		not anchored, matching attempts may take place many times at various
+		positions in the subject, even for a single call. Therefore, if the
+		subject string is very long, it may still pay to use JIT even for
+		one-off matches. JIT support is available for all of the 8-bit, 16-bit
+		and 32-bit PCRE2 libraries and adds about 100KB to the resulting
+		libpcre2.so. JIT support applies only to the traditional Perl-compatible
+		matching function. It does not apply when the DFA matching function is
+		being used.
+
+		Enabling this option can give an about 10x performance increase on JIT
+		operations. It can be desireable for e.g. high performance Apache
+		mod_rewrite or HA-Proxy reqrep operations.
+
+		However, JIT should _only_ be enabled on architectures that are supported.
+		Enabling JIT on unsupported platforms will result in a compilation
+		failure. A list of supported architectures can be found here:
+		https://pcre.org/current/doc/html/pcre2jit.html#SEC2

libs/pcre2/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=pcre2
 PKG_VERSION:=10.32
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=@SF/pcre/$(PKG_NAME)/$(PKG_VERSION)
@@ -25,6 +25,9 @@ PKG_FIXUP:=autoreconf
 PKG_BUILD_PARALLEL:=1
 PKG_INSTALL:=1
 
+PKG_CONFIG_DEPENDS:=\
+	CONFIG_PCRE2_JIT_ENABLED
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/libpcre2/default
@@ -33,6 +36,10 @@ define Package/libpcre2/default
   URL:=https://www.pcre.org/
 endef
 
+define Package/libpcre2/config
+  source "$(SOURCE)/Config.in"
+endef
+
 define Package/libpcre2
   $(call Package/libpcre2/default)
   TITLE:=A Perl Compatible Regular Expression library
@@ -53,7 +60,8 @@ TARGET_CFLAGS += $(FPIC)
 
 CONFIGURE_ARGS += \
 	--enable-pcre2-16 \
-	--enable-pcre2-32 
+	--enable-pcre2-32 \
+	$(if $(CONFIG_PCRE2_JIT_ENABLED),--enable-jit,--disable-jit)
 
 MAKE_FLAGS += \
 	CFLAGS="$(TARGET_CFLAGS)"