depends: Override default build type for libevent

The `libevent` package defaults to the "Release" build type, which
overrides our per-build-type optimization flags with `-O3`.

To prevent this behavior, set `CMAKE_BUILD_TYPE` to "None", consistent
with how other packages are handled.

depends/packages/libevent.mk

@@ -10,7 +10,7 @@ $(package)_build_subdir=build
 # version as we do in releases. Due to quirks in libevents build system, this
 # is also required to enable support for ipv6. See #19375.
 define $(package)_set_vars
-  $(package)_config_opts=-DEVENT__DISABLE_BENCHMARK=ON -DEVENT__DISABLE_OPENSSL=ON
+  $(package)_config_opts=-DCMAKE_BUILD_TYPE=None -DEVENT__DISABLE_BENCHMARK=ON -DEVENT__DISABLE_OPENSSL=ON
   $(package)_config_opts+=-DEVENT__DISABLE_SAMPLES=ON -DEVENT__DISABLE_REGRESS=ON
   $(package)_config_opts+=-DEVENT__DISABLE_TESTS=ON -DEVENT__LIBRARY_TYPE=STATIC
   $(package)_cppflags += -D_GNU_SOURCE