[CI] Disable PIE on Linux Premerge Builds

We do not gain any additional security from having PIE on the test
binaries, and this does have an impact on test times. It is about 10%
from my measurements. Not as much as previous reports
(https://reviews.llvm.org/D140880), but still significant. This is a
similar gain to finish enabling the lit internal shell, which will take
significantly more effort.

Author: boomanaiden154

.ci/monolithic-linux.sh

@@ -60,7 +60,8 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -D MLIR_ENABLE_BINDINGS_PYTHON=ON \
       -D LLDB_ENABLE_PYTHON=ON \
       -D LLDB_ENFORCE_STRICT_TEST_REQUIREMENTS=ON \
-      -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}"
+      -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+      -D CMAKE_EXE_LINKER_FLAGS="-no-pie"
 
 start-group "ninja"