buildsys: allow overriding Julia config via env vars

configure.ac

@@ -793,30 +793,40 @@ AS_IF([test "x$with_julia" != xno ],[
   AS_IF([test "x$JULIA" = x],[ AC_MSG_ERROR([no julia executable found]) ])
 
   AC_MSG_CHECKING([for Julia version])
-  JULIA_VERSION=$(${JULIA} --startup-file=no -e 'print("$(VERSION.major).$(VERSION.minor)")')
-  AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain Julia version])])
+  AS_IF([test "x$JULIA_VERSION" = x],[
+    JULIA_VERSION=$(${JULIA} --startup-file=no -e 'print("$(VERSION.major).$(VERSION.minor)")')
+    AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain Julia version])])
+  ])
   AC_MSG_RESULT([${JULIA_VERSION}])
 
   JL_SHARE=$($JULIA --startup-file=no -e 'print(joinpath(Sys.BINDIR, Base.DATAROOTDIR, "julia"))')
-  AS_IF([test -f "${JL_SHARE}/julia-config.jl"], [], [AC_MSG_ERROR([no julia-config.jl found])])
 
   AC_MSG_CHECKING([for JULIA_CFLAGS])
-  JULIA_CFLAGS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --cflags 2>/dev/null)
-  JULIA_CFLAGS=${JULIA_CFLAGS/-std=gnu99/}  # need to remove -std=gnu99 for our C11 and C++ code
-  AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_CFLAGS from julia-config.jl])])
+  AS_IF([test "x$JULIA_CFLAGS" = x],[
+    AS_IF([test -f "${JL_SHARE}/julia-config.jl"], [], [AC_MSG_ERROR([no julia-config.jl found])])
+    JULIA_CFLAGS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --cflags 2>/dev/null)
+    JULIA_CFLAGS=${JULIA_CFLAGS/-std=gnu99/}  # need to remove -std=gnu99 for our C11 and C++ code
+    AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_CFLAGS from julia-config.jl])])
+  ])
   AC_MSG_RESULT([${JULIA_CFLAGS}])
 
   AC_MSG_CHECKING([for JULIA_LDFLAGS])
-  JULIA_LDFLAGS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --ldflags)
-  AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_LDFLAGS from julia-config.jl])])
-  JULIA_LDFLAGS=${JULIA_LDFLAGS//\'/}
+  AS_IF([test "x$JULIA_LDFLAGS" = x],[
+    AS_IF([test -f "${JL_SHARE}/julia-config.jl"], [], [AC_MSG_ERROR([no julia-config.jl found])])
+    JULIA_LDFLAGS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --ldflags)
+    AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_LDFLAGS from julia-config.jl])])
+    JULIA_LDFLAGS=${JULIA_LDFLAGS//\'/}
+  ])
   AC_MSG_RESULT([${JULIA_LDFLAGS}])
 
   AC_MSG_CHECKING([for JULIA_LIBS])
-  JULIA_LIBS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --ldlibs)
-  AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_LIBS from julia-config.jl])])
-  # remove apostrophes, they confuse libtool in some cases.
-  JULIA_LIBS=${JULIA_LIBS//\'/}
+  AS_IF([test "x$JULIA_LIBS" = x],[
+    AS_IF([test -f "${JL_SHARE}/julia-config.jl"], [], [AC_MSG_ERROR([no julia-config.jl found])])
+    JULIA_LIBS=$(${JULIA} --startup-file=no ${JL_SHARE}/julia-config.jl --ldlibs)
+    AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_LIBS from julia-config.jl])])
+    # remove apostrophes, they confuse libtool in some cases.
+    JULIA_LIBS=${JULIA_LIBS//\'/}
+  ])
   AC_MSG_RESULT([${JULIA_LIBS}])
 ],
 [