download PCRE from sourceforge instead: ftp.pcre.org is dead

Summary:
ftp.pcre.org is dead. We are currently migrating from PCRE1 to
PCRE2. In the meantime, download from SourceForge instead like we do
with Boost.

Reviewed By: akushner, xavierd

Differential Revision: D32520283

fbshipit-source-id: 9fda6930d7d8b677786a43419c4c0dc6289305f1

build/fbcode_builder/manifests/pcre

@@ -9,7 +9,7 @@ pcre-static
 libpcre3-dev
 
 [download]
-url = https://ftp.pcre.org/pub/pcre/pcre-8.43.tar.gz
+url = https://versaweb.dl.sourceforge.net/project/pcre/pcre/8.43/pcre-8.43.tar.gz
 sha256 = 0b8e7465dc5e98c757cc3650a20a7843ee4c3edf50aaf60bb33fd879690d2c73
 
 [build]