Ignore set but empty CORES variable

Change the behavior when the CORES environment variable
is set and empty.
Now `-j` will not be added to make/ninja.

build-compiler-rt.sh

@@ -123,7 +123,7 @@ for arch in $ARCHS; do
         -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS" \
         -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         $SRC_DIR
-    $BUILDCMD ${CORES+-j$CORES}
+    $BUILDCMD ${CORES:+-j${CORES}}
     $BUILDCMD install
     mkdir -p "$PREFIX/$arch-w64-mingw32/bin"
     if [ -n "$SANITIZERS" ]; then

build-libcxx.sh

@@ -114,7 +114,7 @@ for arch in $ARCHS; do
         -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         ..
 
-    $BUILDCMD ${CORES+-j$CORES}
+    $BUILDCMD ${CORES:+-j${CORES}}
     $BUILDCMD install
     cd ..
 done

build-lldb-mi.sh

@@ -147,4 +147,4 @@ cmake \
     $CMAKEFLAGS \
     ..
 
-$BUILDCMD ${CORES+-j$CORES} install/strip
+$BUILDCMD ${CORES:+-j${CORES}} install/strip

build-llvm.sh

@@ -309,6 +309,6 @@ cmake \
     $CMAKEFLAGS \
     ..
 
-$BUILDCMD ${CORES+-j$CORES} install/strip
+$BUILDCMD ${CORES:+-j${CORES}} install/strip
 
 cp ../LICENSE.TXT $PREFIX

build-openmp.sh

@@ -95,7 +95,7 @@ for arch in $ARCHS; do
         -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         $CMAKEFLAGS \
         ..
-    $BUILDCMD ${CORES+-j$CORES}
+    $BUILDCMD ${CORES:+-j${CORES}}
     $BUILDCMD install
     rm -f $PREFIX/$arch-w64-mingw32/bin/*iomp5md*
     rm -f $PREFIX/$arch-w64-mingw32/lib/*iomp5md*