Wipe the cmake cache before rerunning cmake

When rebuilding in an already built directory, cmake does use
the cache file, containing what variables were set to previously.
When changing build configuration (building with a different prefix,
or changing build configurations) this can often result in failed
cmake runs.

Wipe the cache (and the rest of the cmake temp files) by default.
This makes sure that the full cmake configuration is run each time
when running the build scripts, just like it does the first time.
(This doesn't remove the build artifacts; if nothing of significance
has changed, ninja would still reuse old built files.)

By setting the env variable NO_RECONF, this behaviour can be skipped,
rerunning cmake without wiping the cache inbetween. (For cases where
the user knows that the configuration hasn't changed since the last
build, this can speed up the cmake execution time a bit.)

build-compiler-rt.sh

@@ -96,6 +96,7 @@ for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf build-$arch$BUILD_SUFFIX
     mkdir -p build-$arch$BUILD_SUFFIX
     cd build-$arch$BUILD_SUFFIX
+    [ -n "$NO_RECONF" ] || rm -rf CMake*
     cmake \
         ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \
         -DCMAKE_BUILD_TYPE=Release \

build-libcxx.sh

@@ -83,6 +83,7 @@ for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf build-$arch
     mkdir -p build-$arch
     cd build-$arch
+    [ -n "$NO_RECONF" ] || rm -rf CMake*
     cmake \
         ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \
         -DCMAKE_BUILD_TYPE=Release \

build-lldb-mi.sh

@@ -112,6 +112,7 @@ cd lldb-mi
 [ -z "$CLEAN" ] || rm -rf $BUILDDIR
 mkdir -p $BUILDDIR
 cd $BUILDDIR
+[ -n "$NO_RECONF" ] || rm -rf CMake*
 cmake \
     ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \
     -DCMAKE_INSTALL_PREFIX="$PREFIX" \

build-llvm.sh

@@ -292,6 +292,7 @@ fi
 [ -z "$CLEAN" ] || rm -rf $BUILDDIR
 mkdir -p $BUILDDIR
 cd $BUILDDIR
+[ -n "$NO_RECONF" ] || rm -rf CMake*
 # Building LLDB for macOS fails unless building libc++ is enabled at the
 # same time, or unless the LLDB tests are disabled.
 cmake \

build-openmp.sh

@@ -86,6 +86,7 @@ for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf build-$arch
     mkdir -p build-$arch
     cd build-$arch
+    [ -n "$NO_RECONF" ] || rm -rf CMake*
 
     cmake \
         ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \