mkversion.sh: now regenerates version_pm3.c (and consequently the binaries) only when needed

and add --force to forcibly regenerate version_pm3.c

and small fixes:
* document mkversion.sh usage
* remove call to mkversion.sh in client/experimental_lib/CMakeLists.txt on release
* remove call to old `mkversion.pl` in bootrom/Makefile
* just in case, mkversion.sh takes care of atomic write of the file

tools/mkversion.sh

@@ -1,5 +1,13 @@
 #!/usr/bin/env sh
 
+if [ "$1" = "--help" ] || [ "$1" = "-h" ] || [ "$1" = "" ]; then
+    echo "To report a short string about the current version:"
+    echo "   $0 --short"
+    echo "To regenerate version_pm3.c if needed:"
+    echo "   $0 [--force] [--undecided] path/to/version_pm3.c"
+    exit 0
+fi
+
 # Output a version_pm3.c file that includes information about the current build
 # From mkversion.pl
 # pure sh POSIX as now even on Windows we use WSL or ProxSpace with sh available
@@ -13,6 +21,27 @@ if [ "$1" = "--short" ]; then
     SHORT=true
     shift
 fi
+FORCE=false
+if [ "$1" = "--force" ]; then
+    FORCE=true
+    shift
+fi
+UNDECIDED=false
+if [ "$1" = "--undecided" ]; then
+    UNDECIDED=true
+    shift
+fi
+VERSIONSRC="$1"
+
+if ! $SHORT && [ "$VERSIONSRC" = "" ]; then
+    echo "Error: $0 is missing its destination filename"
+    exit 1
+fi
+
+if $SHORT && [ "$VERSIONSRC" != "" ]; then
+    echo "Error: can't output a short string and generate file at the same time"
+    exit 1
+fi
 
 # if you are making your own fork,  change this line to reflect your fork-name
 fullgitinfo="Iceman"
@@ -27,7 +56,7 @@ if [ "$commandGIT" != "" ]; then
     # now avoiding the "fatal: No names found, cannot describe anything." error by fallbacking to abbrev hash in such case
     gitversion=$(git describe --dirty --always)
     gitbranch=$(git rev-parse --abbrev-ref HEAD)
-    if [ "$1" != "--undecided" ]; then
+    if $UNDECIDED; then
         if [ "$gitversion" != "${gitversion%-dirty}" ]; then
             clean=0
         else
@@ -68,7 +97,21 @@ sha=$(
 if [ "$sha" = "" ]; then
   sha="no sha256"
 fi
-cat <<EOF
+
+REDO=true
+if ! $FORCE && [ -f "$VERSIONSRC" ]; then
+    # version src file exists, check if it needs to be updated
+    # file parser quite fragile, be careful if you edit VERSIONSRC template below...
+    oldclean=$(sed '13s/.*\([0-9]\+\).*/\1/;13!d' "$VERSIONSRC")
+    oldfullgitinfo=$(sed '14s/.*"\([^"]*\)".*/\1/;14!d' "$VERSIONSRC")
+    oldsha=$(sed '16s/.*"\([^"]*\)".*/\1/;16!d' "$VERSIONSRC")
+    if [ "$oldclean" = "$clean" ] && [ "$oldfullgitinfo" = "$fullgitinfo" ] && [ "$oldsha" = "$sha" ]; then
+        REDO=false
+    fi
+fi
+if $REDO; then
+    # use a tmp file to avoid concurrent call to mkversion to parse a half-written file.
+    cat > "${VERSIONSRC}.tmp" <<EOF
 #include "common.h"
 /* Generated file, do not edit */
 #ifndef ON_DEVICE
@@ -87,3 +130,5 @@ const struct version_information_t SECTVERSINFO g_version_information = {
     "$sha"
 };
 EOF
+    mv "${VERSIONSRC}.tmp" "${VERSIONSRC}"
+fi