Merge bitcoin#21942: docs: improve make with parallel jobs description.

07bc22e docs: improve make with parallel jobs description. (Klement Tan)

Pull request description:

  Changed `use -jX here for parallelism` to `use "-j N" for N parallel jobs`

  **Rationale**: In my opinion `use -jX here for parallelism` is quite ambiguous as it could be perceived as a single option without any argument. Ie running:
  ```sh
  make -jX
  ```

  Embarrassingly this caused me to be stuck for quite a long time until I opened the help menu for `make` but if I am the only one who faced this issue I would be happy to close this PR.

ACKs for top commit:
  jarolrod:
    ACK 07bc22e

Tree-SHA512: 2d119b6a461668906c63184b865d2cc9fb2f75abeba34e2e44bc1ef3bcb4adec4a49896ddaf3cc6a20c0095ad20d0de0908401b351eaca9443161d24d6b20d0b

doc/build-freebsd.md

@@ -131,6 +131,6 @@ This explicitly enables the GUI and disables legacy wallet support. If `qt5` is
 **Important**: Use `gmake` (the non-GNU `make` will exit with an error).
 
 ```bash
-gmake # use -jX here for parallelism
+gmake # use "-j N" for N parallel jobs
 gmake check # Run tests if Python 3 is available
 ```

doc/build-netbsd.md

@@ -79,6 +79,6 @@ Without wallet:
 
 Build and run the tests:
 ```bash
-gmake # use -jX here for parallelism
+gmake # use "-j N" here for N parallel jobs
 gmake check
 ```

doc/build-openbsd.md

@@ -85,7 +85,7 @@ To configure with GUI:
 
 Build and run the tests:
 ```bash
-gmake # use -jX here for parallelism
+gmake # use "-j N" here for N parallel jobs
 gmake check
 ```
 

doc/build-osx.md

@@ -276,7 +276,7 @@ After configuration, you are ready to compile.
 Run the following in your terminal to compile Dash Core:
 
 ``` bash
-make -jx    # use -jX here for parallelism
+make        # use "-j N" here for N parallel jobs
 make check  # Run tests if Python 3 is available
 ```
 

doc/build-unix.md

@@ -22,7 +22,7 @@ To Build
 ```sh
 ./autogen.sh
 ./configure
-make
+make # use "-j N" for N parallel jobs
 make install # optional
 ```