ci: make p4 setup on macOS more robust

When setting up Perforce on macOS we put both `p4` and `p4d` into
"$HOME/bin". On GitHub CI this directory is indeed contained in the PATH
environment variable and thus there is no need for additional setup than
to put the binaries there. But GitLab CI does not do this, and thus our
Perforce-based tests would be skipped there even though we download the
binaries.

Refactor the setup code to become more robust by downloading binaries
into a separate directory which we then manually append to our PATH.
This matches what we do on Linux-based jobs.

Note that it may seem like we already did append "$HOME/bin" to PATH
because we're actually removing the lines that adapt PATH. But we only
ever adapted the PATH variable in "ci/install-dependencies.sh", and
didn't adapt it when running "ci/run-build-and-test.sh". Consequently,
the required binaries wouldn't be found during the test run unless the
CI platform already had the "$HOME/bin" in PATH right from the start.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/install-dependencies.sh

@@ -37,15 +37,13 @@ macos-*)
 	test -z "$BREW_INSTALL_PACKAGES" ||
 	brew install $BREW_INSTALL_PACKAGES
 	brew link --force gettext
-	mkdir -p $HOME/bin
-	(
-		cd $HOME/bin
+
+	mkdir -p "$P4_PATH"
+	pushd "$P4_PATH"
 		wget -q "$P4WHENCE/bin.macosx1015x86_64/helix-core-server.tgz" &&
 		tar -xf helix-core-server.tgz &&
 		sudo xattr -d com.apple.quarantine p4 p4d 2>/dev/null || true
-	)
-	PATH="$PATH:${HOME}/bin"
-	export PATH
+	popd
 
 	if test -n "$CC_PACKAGE"
 	then

ci/lib.sh

@@ -344,6 +344,9 @@ macos-*)
 	then
 		MAKEFLAGS="$MAKEFLAGS APPLE_COMMON_CRYPTO_SHA1=Yes"
 	fi
+
+	P4_PATH="$HOME/custom/p4"
+	export PATH="$P4_PATH:$PATH"
 	;;
 esac