winbuild: reduce command-line length by dropping whitespace

Keep the `@for %%i in [...]` lines within limits by stripping whitespace
from the input `.c` source lists read from `Makefile.inc`. To avoid this
error after adding a new `.c` source:
```
configuration name: libcurl-vc14-x64-release-dll-ssl-dll-ipv6-sspi
NMAKE : fatal error U1095: expanded command line 'for %i in (altsvc.obj            amigaos.obj
           asyn-ares.obj         asyn-thread.obj       base64.obj            bufq.obj
              bufref.obj            cf-h1-proxy.obj       cf-h2-proxy.obj       cf-haproxy.obj [...]
  vssh/wolfssh.obj) do @echo ..\builds\libcurl-vc14-x64-release-dll-ssl-dll-ipv6-sspi-obj-lib/%i \
                   ' too long
Stop.
Command exited with code 2
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/51605338/job/dqg6qtebtscb279g#L44

Reported-by: Stefan Eissing
Bug: https://github.com/curl/curl/pull/16508#issuecomment-2690443409
Fixes #16521
Closes #16528

diff --git a/winbuild/Makefile.vc b/winbuild/Makefile.vc
index d404279dd3bd5cc3193519e1150afedc1330ccbe..1f1e6d550c7476a40d89de6dab6494c644b781b0 100644 (file)
--- a/winbuild/Makefile.vc
+++ b/winbuild/Makefile.vc
@@ -58,9 +58,11 @@ CFGSET=true
 !ENDIF
 
 !INCLUDE "../lib/Makefile.inc"
+CSOURCES=$(CSOURCES:  = )
 LIBCURL_OBJS=$(CSOURCES:.c=.obj)
 
 !INCLUDE "../src/Makefile.inc"
+CURL_CFILES=$(CURL_CFILES:  = )
 CURL_OBJS=$(CURL_CFILES:.c=.obj)