[libc++] Silence CMake's install messages in the CI (#128872)

Currently, there are a ton of `-- Installing:` and `-- Up-to-date:`
messages in the CI log, which just clutter the output. This disables
these messages to significantly shorten the CI logs, making them much
faster to load and easier to read.

libcxx/utils/ci/run-buildbot

@@ -127,6 +127,8 @@ function clean() {
 
 function generate-cmake-base() {
     step "Generating CMake"
+
+    # We can remove -DCMAKE_INSTALL_MESSAGE=NEVER once https://gitlab.kitware.com/cmake/cmake/-/issues/26085 is fixed.
     ${CMAKE} \
           -S "${MONOREPO_ROOT}/runtimes" \
           -B "${BUILD_DIR}" \
@@ -136,6 +138,7 @@ function generate-cmake-base() {
           -DLIBCXX_ENABLE_WERROR=YES \
           -DLIBCXXABI_ENABLE_WERROR=YES \
           -DLIBUNWIND_ENABLE_WERROR=YES \
+          -DCMAKE_INSTALL_MESSAGE=NEVER \
           -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
           "${@}"
 }