[CI] Clean up runtimes builds (llvm#131913)

This patch cleans up the runtimes build in premerge due to queuing
delays, dropping the C++03 testing, but keeping the C++20 and Modules
configurations as they are deemed important by clang contributors.

This patch also makes it easier in the future when we need to rework the
runtimes build to anticipate the deprecation of building most of the
runtimes with LLVM_ENABLE_PROJECTS.

Author: boomanaiden154

.ci/monolithic-linux.sh

@@ -90,23 +90,6 @@ if [[ "${runtimes}" != "" ]]; then
   INSTALL_DIR="${BUILD_DIR}/install"
   mkdir -p ${RUNTIMES_BUILD_DIR}
 
-  echo "--- cmake runtimes C++03"
-
-  cmake -S "${MONOREPO_ROOT}/runtimes" -B "${RUNTIMES_BUILD_DIR}" -GNinja \
-      -D CMAKE_C_COMPILER="${INSTALL_DIR}/bin/clang" \
-      -D CMAKE_CXX_COMPILER="${INSTALL_DIR}/bin/clang++" \
-      -D LLVM_ENABLE_RUNTIMES="${runtimes}" \
-      -D LIBCXX_CXX_ABI=libcxxabi \
-      -D CMAKE_BUILD_TYPE=RelWithDebInfo \
-      -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
-      -D LIBCXX_TEST_PARAMS="std=c++03" \
-      -D LIBCXXABI_TEST_PARAMS="std=c++03" \
-      -D LLVM_LIT_ARGS="${lit_args}"
-
-  echo "--- ninja runtimes C++03"
-
-  ninja -vC "${RUNTIMES_BUILD_DIR}" ${runtime_targets}
-
   echo "--- cmake runtimes C++26"
 
   rm -rf "${RUNTIMES_BUILD_DIR}"
@@ -140,6 +123,6 @@ if [[ "${runtimes}" != "" ]]; then
       -D LLVM_LIT_ARGS="${lit_args}"
 
   echo "--- ninja runtimes clang modules"
-  
+
   ninja -vC "${RUNTIMES_BUILD_DIR}" ${runtime_targets}
 fi