Enable builds from local llvm-project tree

In order to use a local git tree we need to provide a customized
`version.spec.inc` and we need to avoid downloading any tarball from
github but build our own. This can be achieved with this command:

```
make mockbuild-snapshot GIT_TREE=~/llvm-project
```

A sample output could look like this:

```
$ make mockbuild-snapshot GIT_TREE=~/src/llvm-project/main
Creating tarball from git tree: /home/kkleine/src/llvm-project/main
YYYYMMDD=20250115 GIT_TREE=/home/kkleine/src/llvm-project/main ./.copr/snapshot-info.sh > /home/kkleine/src/llvm-rpms/llvm-big-merge/version.spec.inc
[INFO] Gathering snapshot info from here: /home/kkleine/src/llvm-project/main
[INFO] Determine date in YYYYMMDD form
%global maj_ver 20
%global min_ver 0
%global patch_ver 0
%undefine rc_ver

%global llvm_snapshot_version            20.0.0
%global llvm_snapshot_version_major      20
%global llvm_snapshot_version_minor      0
%global llvm_snapshot_version_patch      0
%global llvm_snapshot_yyyymmdd           20250115
%global llvm_snapshot_git_revision       f579320b5eb348a68298d5a78ae849dcbbf37aa2
%global llvm_snapshot_git_revision_short f579320b5eb348
%global llvm_snapshot_version_suffix     pre20250115.gf579320b5eb348
git -C /home/kkleine/src/llvm-project/main archive --format=tar.gz -o /home/kkleine/src/llvm-rpms/llvm-big-merge/f579320b5eb348a68298d5a78ae849dcbbf37aa2.tar.gz --prefix=llvm-project-f579320b5eb348a68298d5a78ae849dcbbf37aa2/ HEAD
rpmbuild \
	--with=snapshot_build \
	--define "_rpmdir /home/kkleine/src/llvm-rpms/llvm-big-merge" \
	--define "_sourcedir /home/kkleine/src/llvm-rpms/llvm-big-merge" \
	--define "_specdir /home/kkleine/src/llvm-rpms/llvm-big-merge" \
	--define "_srcrpmdir /home/kkleine/src/llvm-rpms/llvm-big-merge" \
	--define "_builddir /home/kkleine/src/llvm-rpms/llvm-big-merge" \
	-bs llvm.spec
[...CUT OF BUILD LOG ...]
```

Author: kwk

.copr/snapshot-info.sh

@@ -13,18 +13,40 @@ function loginfo() {
     >&2 echo "[INFO]" $msg
 }
 
+function logerr() {
+    local msg=$1
+    >&2 echo "[ERROR]" $msg
+}
+
+# Check if we shall gather versioning information from a supplied git tree
+if [ "$GIT_TREE" != "" ]; then
+    loginfo "Gathering snapshot info from here: $GIT_TREE"
+    if [ "$(git -C $GIT_TREE  rev-parse --is-inside-work-tree 2>/dev/null)" != "true" ]; then
+        logerr "Not a git directory: $GIT_TREE"
+        exit 1
+    fi
+    llvm_snapshot_git_revision=$(git -C $GIT_TREE rev-parse HEAD)
+    versionfile=$GIT_TREE/cmake/Modules/LLVMVersion.cmake
+    llvm_snapshot_version=`grep -ioP 'set\(\s*LLVM_VERSION_(MAJOR|MINOR|PATCH)\s\K[0-9]+' ${versionfile} | paste -sd '.'`
+fi
+
 loginfo "Determine date in YYYYMMDD form"
 llvm_snapshot_yyyymmdd=$(date +%Y%m%d)
 [[ ! -z "${YYYYMMDD}" ]] && llvm_snapshot_yyyymmdd=$YYYYMMDD
 
-git_revision_url=https://github.com/fedora-llvm-team/llvm-snapshots/releases/download/snapshot-version-sync/llvm-git-revision-${llvm_snapshot_yyyymmdd}.txt
-loginfo "Get the revision for today from $git_revision_url"
-llvm_snapshot_git_revision=$(curl -sL $git_revision_url)
+if [ -z $GIT_TREE ]; then
+    git_revision_url=https://github.com/fedora-llvm-team/llvm-snapshots/releases/download/snapshot-version-sync/llvm-git-revision-${llvm_snapshot_yyyymmdd}.txt
+    loginfo "Get the revision for today from $git_revision_url"
+    llvm_snapshot_git_revision=$(curl -sL $git_revision_url)
+fi
 llvm_snapshot_git_revision_short=$(echo "${llvm_snapshot_git_revision:0:14}")
 
-release_url=https://github.com/fedora-llvm-team/llvm-snapshots/releases/download/snapshot-version-sync/llvm-release-${llvm_snapshot_yyyymmdd}.txt
-loginfo "Get the release for today from $release_url"
-llvm_snapshot_version=$(curl -sL $release_url)
+
+if [ -z $GIT_TREE ]; then
+    release_url=https://github.com/fedora-llvm-team/llvm-snapshots/releases/download/snapshot-version-sync/llvm-release-${llvm_snapshot_yyyymmdd}.txt
+    loginfo "Get the release for today from $release_url"
+    llvm_snapshot_version=$(curl -sL $release_url)
+fi
 llvm_snapshot_version_major=$(echo $llvm_snapshot_version | cut -f1 -d.)
 llvm_snapshot_version_minor=$(echo $llvm_snapshot_version | cut -f2 -d.)
 llvm_snapshot_version_patch=$(echo $llvm_snapshot_version | cut -f3 -d.)

Makefile

@@ -9,17 +9,27 @@ MOCK_OPTS_SNAPSHOT?=$(MOCK_OPTS_RELEASE) --with snapshot_build $(MOCK_OPTS)
 YYYYMMDD?=$(shell date +%Y%m%d)
 SOURCEDIR=$(shell pwd)
 SPEC=llvm.spec
-# When nothing is given, this will be determined based on
-# release or snapshot builds.
+# When nothing is given, this will be determined based on release or snapshot
+# builds.
 SRPM_PATH?=
+# Provide a path to your local llvm-project clone to build a snapshot of that
+# tree.
+GIT_TREE?=
 
 ######### Get sources
 
 .PHONY: get-sources-snapshot
 ## Downloads all sources we need for a snapshot build.
 get-sources-snapshot:
-	YYYYMMDD=$(YYYYMMDD) ./.copr/snapshot-info.sh > $(SOURCEDIR)/version.spec.inc
+	YYYYMMDD=$(YYYYMMDD) GIT_TREE=$(GIT_TREE) ./.copr/snapshot-info.sh > $(SOURCEDIR)/version.spec.inc
+ifeq ($(GIT_TREE),)
 	spectool -g --define "_sourcedir $(SOURCEDIR)" --define "_with_snapshot_build 1" $(SPEC)
+else
+	$(info Creating tarball from git tree: $(GIT_TREE))
+	$(eval llvm_snapshot_git_revision:=$(shell git -C $(GIT_TREE) rev-parse HEAD))
+	git -C $(GIT_TREE) archive --format=tar.gz -o $(PWD)/$(llvm_snapshot_git_revision).tar.gz --prefix=llvm-project-$(llvm_snapshot_git_revision)/ HEAD
+endif
+
 
 .PHONY: get-sources-release
 ## Downloads all sources we need for a release build.