autotools: simplify configuration in tests, examples

- GHA/windows: make a mingw autotools build static only.
- GHA/windows: fix a CI script issue with the build above.
- src: fix to pass `LIBCURL_PC_LIBS_PRIVATE` instead of `LINKFLAGS`.
  This makes the libs propagate to tunits, making the local hack there
  unnecessary. `LINKFLAGS` had this single use in the repo, and it was
  empty in local tests.
- tests: drop passing redundant `LIBCURL_PC_LDFLAGS_PRIVATE`.
- tests: drop redundant target name from config variables.
- examples, tests/client: drop `LIBDIR` temp variables with single uses.
- examples, tests: formatting to sync `Makefile.am` scripts with each
  other.

Closes #17661

tests/server/Makefile.am

@@ -53,16 +53,14 @@ LIBS = $(BLANK_AT_MAKETIME)
 if DOING_NATIVE_WINDOWS
 AM_CPPFLAGS += -DCURL_STATICLIB
 endif
-
 AM_CPPFLAGS += -DWITHOUT_LIBCURL -DCURL_NO_OLDIES
 
 $(BUNDLE_SRC): $(top_srcdir)/scripts/mk-unity.pl Makefile.inc $(FIRSTFILES) $(UTILS) $(CURLX_SRCS) $(TESTFILES)
 	@PERL@ $(top_srcdir)/scripts/mk-unity.pl --include $(UTILS) $(CURLX_SRCS) --test $(TESTFILES) > $(BUNDLE_SRC)
 
 noinst_PROGRAMS = $(BUNDLE)
-nodist_servers_SOURCES = $(BUNDLE_SRC)
-servers_LDADD = @CURL_NETWORK_AND_TIME_LIBS@
-servers_CFLAGS = $(AM_CFLAGS)
+nodist_SOURCES = $(BUNDLE_SRC)
+LDADD = @CURL_NETWORK_AND_TIME_LIBS@
 CLEANFILES = $(BUNDLE_SRC)
 
 CHECKSRC = $(CS_$(V))