sysinfo.gap: add GAP and GAC variables

... and use them in `bin/BuildPackages.sh` and `etc/Makefile.gappkg`.

This strengthen the purpose of sysinfo.gap: that in order to build a
package (or anything that wants to interact with GAP), you just point it
at the sysinfo.gap of the target GAP installation, and it extracts all
it needs from there, including the location of a GAP and GAC executable.

Note that sysinfo.gap can be directly included from POSIX shell scripts
and Makefiles, and it is also fairly easy to parse for other systems.

Makefile.rules

@@ -724,6 +724,9 @@ GAP_KERNEL_MINOR_VERSION=$(GAP_KERNEL_MINOR_VERSION)
 GAP_BIN_DIR="$(abs_builddir)"
 GAP_LIB_DIR="$(abs_srcdir)"
 
+GAP="$(abs_builddir)/bin/gap.sh"
+GAC="$(abs_builddir)/gac"
+
 GAP_CC="$(CC)"
 GAP_CXX="$(CXX)"
 GAP_CFLAGS="$(GAP_CFLAGS)"

bin/BuildPackages.sh

@@ -48,8 +48,8 @@ while [[ "$#" -ge 1 ]]; do
     --with-gaproot=*) GAPROOT=${option#--with-gaproot=}; ;;
     --parallel)       PARALLEL=yes; ;;
 
-    --with-gap)       GAP="$1"; shift ;;
-    --with-gap=*)     GAP=${option#--with-gap=}; ;;
+    --with-gap)       GAP_EXE="$1"; shift ;;
+    --with-gap=*)     GAP_EXE=${option#--with-gap=}; ;;
 
     --no-color)       COLORS=no ;;
     --color)          COLORS=yes ;;
@@ -63,8 +63,6 @@ while [[ "$#" -ge 1 ]]; do
   esac
 done
 
-GAP="${GAP:-$GAPROOT/bin/gap.sh}"
-
 if [ "x$PARALLEL" = "xyes" ]; then
   export MAKEFLAGS="${MAKEFLAGS:--j3}"
 fi;
@@ -110,6 +108,20 @@ fi
 # read in sysinfo
 source "$GAPROOT/sysinfo.gap"
 
+# determine the GAP executable to call:
+# - if the user specified one explicitly via the `--gap` option, then
+#   GAP_EXE is set and we should use that
+# - otherwise if sysinfo.gap set the GAP variable, use that
+# - otherwise fall back to $GAPROOT/bin/gap.sh
+if [[ -n $GAP_EXE ]]
+then
+  GAP="$GAP_EXE"
+else
+  GAP="${GAP:-$GAPROOT/bin/gap.sh}"
+fi
+
+
+
 # detect whether GAP was built in 32bit mode
 # TODO: once all packages have adapted to the new build system,
 # this should no longer be necessary, as package build systems should

etc/Makefile.gappkg

@@ -50,9 +50,6 @@ endif
 KEXT_BINARCHDIR = bin/$(GAParch)
 KEXT_SO = $(KEXT_BINARCHDIR)/$(KEXT_NAME).so
 
-GAP = $(GAPPATH)/gap
-GAC = $(GAPPATH)/gac
-
 # override KEXT_RECONF if your package needs a different invocation
 # for reconfiguring (e.g. `./config.status --recheck` for autoconf)
 ifdef KEXT_USE_AUTOCONF