Configure fails on --with-target-bits=32 for Windows since it tries to locate the non-existing 32-bit version of vcruntime140_1.dll. This is not needed on 32 bit and should be skipped.

In JDK 16+, this seems to be implicitly fixed with JDK-8248238:
  https://github.com/openjdk/jdk/commit/9604ee82#diff-faa23e14e93e8ccffb102d4696b367b75f88ae8dcc91b02b473bdc69b4a7b786R734

...and followup in JDK-8257679:
  https://github.com/openjdk/jdk/commit/d29c78da#diff-9ae6a9495d0da7dfc02e8d804de187641e8dd59c7ae671ac2170c21d4c6204e2R607

JDK 15 Windows 32 builds still fail, and may need a point fix like this:

diff -r c5dd31945532 make/autoconf/toolchain_windows.m4
--- a/make/autoconf/toolchain_windows.m4 Wed Jan 20 17:26:13 2021 +0000
+++ b/make/autoconf/toolchain_windows.m4 Mon Feb 08 19:15:25 2021 +0100
@@ -807,7 +807,7 @@
   AC_ARG_WITH(vcruntime-1-dll, [AS_HELP_STRING([--with-vcruntime-1-dll],
       [path to microsoft C++ runtime dll (vcruntime*_1.dll) (Windows only) @<:@probed@:>@])])
 
- if test "x$VCRUNTIME_1_NAME" != "x"; then
+ if test "x$VCRUNTIME_1_NAME" != "x" && test "x$OPENJDK_TARGET_CPU" = xx86_64; then
     if test "x$with_vcruntime_1_dll" != x; then
       # If given explicitly by user, do not probe. If not present, fail directly.
       TOOLCHAIN_CHECK_POSSIBLE_MSVC_DLL($VCRUNTIME_1_NAME, [$with_vcruntime_1_dll],

With the patch above, JDK 15 Windows 32 builds work.