bootstrap: Fix running multiple times in-source

Since commit v3.9.0-rc1~281^2 (Use quotes for non-system includes,
2017-04-11) we include `cmConfigure.h` via `""` instead of `<>`.
This breaks the `bootstrap` script when run more than once in an
in-source build.  In that case `cmConfigure.h` is generated next
to the source files that include it, so `""`-style includes prevent the
`Bootstrap.cmk/cmConfigure.h` file from being included during bootstrap.

Fix this by teaching the bootstrap script to remove any `cmConfigure.h`
that may have been generated by an earlier run in an in-source build.

Fixes: #17082

bootstrap

@@ -830,6 +830,12 @@ rm -f "${cmake_bootstrap_dir}/cmake_bootstrap.log"
 rm -f "${cmake_bootstrap_dir}/cmConfigure.h${_tmp}"
 rm -f "${cmake_bootstrap_dir}/cmVersionConfig.h${_tmp}"
 
+# If building in-source, remove any cmConfigure.h that may
+# have been created by a previous run of the bootstrap cmake.
+if [ -n "${cmake_in_source_build}" ]; then
+  rm -f "${cmake_source_dir}/Source/cmConfigure.h"
+fi
+
 # If exist compiler flags, set them
 cmake_c_flags=${CFLAGS}
 cmake_cxx_flags=${CXXFLAGS}