configure: add -static suffix to internal static libs for test programs

In MSVC builds, object files built for shared or static libraries are
technically not compatible with each other. That's why building both
shared and static libraries simultaneously is not allowed in configure.
This may change in the future once dllimport/dllexport attributes are no
longer used. Which will be possible on next major bump. The only
remaining use of dllexport was changed in c6c8063186.

However, for test programs, we still build internal static libraries
that allow the test programs to access internal symbols.

In commit 8eca3fa619, I assumed that when
CONFIG_STATIC=0, we would never build a static library. We actually do
build one for internal purposes, for the test executables. In that case,
we only link the tested library statically (using the same object files
as built for the shared library), the rest of the libraries are still
linked dynamically.

Such libraries are never installed and are used only for test programs.
This change adds a -static suffix to these internal libraries to avoid
name conflicts. In the MSVC world, static libraries and import libraries
are generally the same thing and share the same naming conventions.

Fixes: 8eca3fa619
Signed-off-by: Kacper Michajłow <kasper93@gmail.com>

configure

@@ -6066,16 +6066,17 @@ case $target_os in
         ;;
     win32|win64)
         disable symver
+        LIBSUF=".lib"
         if enabled shared; then
             # Cannot build both shared and static libs with MSVC or icl.
             disable static
+            LIBSUF="-static.lib"
         fi
         ! enabled small && test_cmd $windres --version && enable gnu_windres
         enabled x86_32 && check_ldflags -LARGEADDRESSAWARE
         add_cppflags -DWIN32_LEAN_AND_MEAN
         shlibdir_default="$bindir_default"
         LIBPREF=""
-        LIBSUF=".lib"
         SLIBPREF=""
         SLIBSUF=".dll"
         SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'