Uhm... well no idea, sorry. MSVC sometimes freaks the shit out of me.
We'll probably have to wait for a patch from the Windows folks.

Maybe moving line 1768 to 1765 fixes that?
But if, you'll probably still need the config.w32 from trunk.

Yesterday (before) the release I compiled from trunk with the same errors. That was about 10 hours after you promoted 2.0 to trunk. I will try trunk as I see you have tried to fix it.

The windows build box currently generates binaires successfully, though:
http://windows.php.net/downloads/pecl/snaps/http/2.0.0/

But it that with Curl, Propo and Raphf enabled?

Result after moving line 1768 to 1765: A few warnings, but it builds. Time for 2.0.1!

   Creating library Release\php_curl.lib and object Release\php_curl.exp
   Creating library Release\php_propro.lib and object Release\php_propro.exp
   Creating library Release\php_raphf.lib and object Release\php_raphf.exp
php_http_client_curl.c
c:\php-sdk\php55dev\ext\http\php_http_misc.h(101) : warning C4018: '<' : signed/
unsigned mismatch
libcurl_a.lib(inflate.obj) : warning LNK4006: _inflateInit2_ already defined in
php5.lib(php5.dll); second definition ignored
libcurl_a.lib(inflate.obj) : warning LNK4006: _inflate already defined in php5.l
ib(php5.dll); second definition ignored
libcurl_a.lib(inflate.obj) : warning LNK4006: _inflateEnd already defined in php
5.lib(php5.dll); second definition ignored
libcurl_a.lib(inflate.obj) : warning LNK4006: _inflateCopy already defined in ph
p5.lib(php5.dll); second definition ignored
libcurl_a.lib(zutil.obj) : warning LNK4006: _zlibVersion already defined in php5
.lib(php5.dll); second definition ignored
libcurl_a.lib(zutil.obj) : warning LNK4006: _zError already defined in php5.lib(
php5.dll); second definition ignored
   Creating library Release\php_http.lib and object Release\php_http.exp
LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; us
e /NODEFAULTLIB:library
Release\php_http.dll : warning LNK4088: image being generated due to /FORCE opti
on; image may not run
EXT http build complete

Yep, pecl_http-2 cannot be built without raphf and propro.

Those linker warnings can be ignored, though. There here since pecl_http links against zlib (early 0. versions).

Before packagaing a 2.0.1 with a fix for a symptom, knowledge about the cause would be awesome though.

Is not 	php_http_client_curl_t *curl a declaration? For MSVC they must be at the beginnen of a block. I will test now if this works as well:

static int php_http_client_curl_once(php_http_client_t *h)
{
	php_http_client_curl_t *curl;
	TSRMLS_FETCH_FROM_CTX(h->ts);

#if PHP_HTTP_HAVE_EVENT
	curl = h->ctx;

BTW: I ran into Propro and aphf yesterday. For Windows users: php_propro.dll and php_raphf.dll must be loaded before php_http.dll.

I checked the php_http.dll from the windows build box. That one does not have libevent support (and is 719KB). My build has libevent 2.0.21-stable and is 791KB).

I now have the code below, which builds fine for PHP 5.3.28-dev, 5.4.22 and 5.5.6.

static STATUS php_http_client_curl_exec(php_http_client_t *h)
{
	php_http_client_curl_t *curl;
	TSRMLS_FETCH_FROM_CTX(h->ts);

#if PHP_HTTP_HAVE_EVENT
	curl = h->ctx;

OK, you moved to git and fixed the issue. Thanks Mike and Anatol.

yes the move to git was long  due.

anatol had a deeper look based on your report, thanks!