Add -j$(nproc) make option to speed up build time (#15928)

Adding `-j$(nproc)` reduces build time on the external dependencies by
approximately 25%.

virtualization/Docker/scripts/libcec

@@ -41,7 +41,7 @@ git submodule update --init src/platform
         -DPYTHON_LIBRARY="${PYTHON_LIBRARY}" \
         -DPYTHON_INCLUDE_DIR="${PYTHON_INCLUDE_DIR}" \
         ..
-    make
+    make -j$(nproc)
     make install
     ldconfig
 )

virtualization/Docker/scripts/openalpr

@@ -26,7 +26,7 @@ cd build
 cmake -DWITH_TEST=FALSE -DWITH_BINDING_JAVA=FALSE --DWITH_BINDING_PYTHON=FALSE --DWITH_BINDING_GO=FALSE -DWITH_DAEMON=FALSE -DCMAKE_INSTALL_PREFIX:PATH=/usr/local ..
 
 # compile the library
-make
+make -j$(nproc)
 
 # Install the binaries/libraries to your local system (prefix is /usr/local)
 make install

virtualization/Docker/scripts/ssocr

@@ -18,7 +18,7 @@ git clone --depth 1 https://github.com/auerswal/ssocr.git ssocr
 cd ssocr/
 
 # Compile the library
-make
+make -j$(nproc)
 
 # Install the binaries/libraries to your local system (prefix is /usr/local)
 make install