[PATCH v5 02/15] cmake: use "-S" and "-B" to specify source and build directories

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Rather than the multi-line "mkdir/cd/cmake" recipe provide an
equivalent one-liner using the "-S" and "-B" options, and then suggest building with "make -C <build-dir>".

The rest of these instructions discuss e.g. running tests from our
top-level "t/" directory, so it's more helpful to avoid changing the
user's current directory.

The "-S" and "-B" options were added in cmake v3.13.0, which is older
than the version we have a hard dependency on[1].

As an aside The "-p" flag to "mkdir" in the pre-image wasn't needed,
as "contrib/buildsystems" is tracked

1. 061c2240b1b (Introduce CMake support for configuring Git, 2020-06-12)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 contrib/buildsystems/CMakeLists.txt | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 8f8b6f375f7..5b22a9b217f 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -16,9 +16,7 @@ though, therefore the `File>Open>Folder...` option is preferred.
 
 Instructions to run CMake manually:
 
-    mkdir -p contrib/buildsystems/out
-    cd contrib/buildsystems/out
-    cmake ../ -DCMAKE_BUILD_TYPE=Release
+    cmake -S contrib/buildsystems -B contrib/buildsystems/out -DCMAKE_BUILD_TYPE=Release
 
 This will build the git binaries in contrib/buildsystems/out
 directory (our top-level .gitignore file knows to ignore contents of
@@ -36,8 +34,8 @@ NOTE: -DCMAKE_BUILD_TYPE is optional. For multi-config generators like Visual St
 this option is ignored
 
 This process generates a Makefile(Linux/*BSD/MacOS) , Visual Studio solution(Windows) by default.
-Run `make` to build Git on Linux/*BSD/MacOS.
-Open git.sln on Windows and build Git.
+Run `make -C contrib/buildsystems/out` to build Git on Linux/*BSD/MacOS.
+Open contrib/buildsystems/git.sln on Windows and build Git.
 
 NOTE: By default CMake uses Makefile as the build tool on Linux and Visual Studio in Windows,
 to use another tool say `ninja` add this to the command line when configuring.
-- 
2.39.0.rc1.981.gf846af54b4b