Resolve hosts by DNS name in separate threads so we can cancel them

getaddrinfo(3) may block a long time so proper termination of the daemon may
block if DNS servers are not reachable.

getaddrinfo(3) is an optional cancellation point in posix threads so it
might still block a shutdown but at least on Android (with the signal based
pthread_cancel implementation) it works, on Linux starter will kill charon
anyway after a while.

src/libstrongswan/Makefile.am

@@ -1,8 +1,8 @@
 ipseclib_LTLIBRARIES = libstrongswan.la
 
 libstrongswan_la_SOURCES = \
-library.c chunk.c debug.c enum.c settings.c printf_hook.c asn1/asn1.c \
-asn1/asn1_parser.c asn1/oid.c bio/bio_reader.c bio/bio_writer.c \
+library.c chunk.c debug.c enum.c host_resolver.c settings.c printf_hook.c \
+asn1/asn1.c asn1/asn1_parser.c asn1/oid.c bio/bio_reader.c bio/bio_writer.c \
 crypto/crypters/crypter.c crypto/hashers/hasher.c crypto/pkcs7.c crypto/pkcs9.c \
 crypto/proposal/proposal_keywords.c crypto/proposal/proposal_keywords_static.c \
 crypto/prfs/prf.c crypto/prfs/mac_prf.c \
@@ -31,7 +31,7 @@ utils/optionsfrom.c utils/capabilities.c utils/backtrace.c utils/tun_device.c
 if USE_DEV_HEADERS
 strongswan_includedir = ${dev_headers}
 nobase_strongswan_include_HEADERS = \
-library.h chunk.h debug.h enum.h settings.h printf_hook.h \
+library.h chunk.h debug.h enum.h host_resolver.h settings.h printf_hook.h \
 asn1/asn1.h asn1/asn1_parser.h asn1/oid.h bio/bio_reader.h bio/bio_writer.h \
 crypto/crypters/crypter.h crypto/hashers/hasher.h crypto/mac.h \
 crypto/pkcs7.h crypto/pkcs9.h crypto/proposal/proposal_keywords.h \