build: Suppress stupid MSVC linker warning

... and use correct format to pass linker flags

.cirrus.yml

@@ -258,7 +258,7 @@ task:
     # Set non-essential options that affect the CLI messages here.
     # (They depend on the user's taste, so we don't want to set them automatically in configure.ac.)
     CFLAGS: -nologo -diagnostics:caret
-    LDFLAGS: -XCClinker -nologo -XCClinker -diagnostics:caret
+    LDFLAGS: -Xlinker -Xlinker -Xlinker -nologo
   matrix:
     - name: "x86_64 (MSVC): Windows (Debian stable, Wine)"
     - name: "x86_64 (MSVC): Windows (Debian stable, Wine, int128_struct)"

configure.ac

@@ -115,6 +115,12 @@ AC_DEFUN([SECP_TRY_APPEND_DEFAULT_CFLAGS], [
     if test x"$GCC" != x"yes" && test x"$build_windows" = x"yes"; then
       SECP_TRY_APPEND_CFLAGS([-W2 -wd4146], $1) # Moderate warning level, disable warning C4146 "unary minus operator applied to unsigned type, result still unsigned"
       SECP_TRY_APPEND_CFLAGS([-external:anglebrackets -external:W0], $1) # Suppress warnings from #include <...> files
+      # We pass -ignore:4217 to the MSVC linker to suppress warning 4217 when
+      # importing variables from a statically linked secp256k1.
+      # (See the libtool manual, section "Windows DLLs" for background.)
+      # Unfortunately, libtool tries to be too clever and strips "-Xlinker arg"
+      # into "arg", so this will be " -Xlinker -ignore:4217" after stripping.
+      LDFLAGS="-Xlinker -Xlinker -Xlinker -ignore:4217 $LDFLAGS" 
     fi
 ])
 SECP_TRY_APPEND_DEFAULT_CFLAGS(SECP_CFLAGS)