mk4build: change how the _FOR_BUILD variables are passed to sub-confi…

…gure

The logic that eval's for *_FOR_BUILD variables to set them to their
equivalent without _FOR_BUILD before calling the sub-configure for the
host machine doesn't work: the variables are not exported, and
therefore they are not seen by the ./configure script, which runs as a
separate process.

So instead, keep things simple and pass them explicitly in the
environment of the ./configure script.

This patch was written in the context of the Buildroot build system,
which does cross-compilation, through which we discovered that the
*_FOR_BUILD variables are not properly passed down to the
sub-configure.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

mk4build

@@ -67,13 +67,12 @@ then
 
    needTemporaryDirectory
 
-   for variable in CC CFLAGS CXX CXXFLAGS LDFLAGS LDLIBS
-   do
-      unset "${variable}"
-      variableForBuild="${variable}_FOR_BUILD"
-      eval test '"${'"${variableForBuild}"'+set}"' != "set" || eval "${variable}"'="${'"${variableForBuild}"'}"'
-   done
-
+   CC=${CC_FOR_BUILD} \
+   CFLAGS=${CFLAGS_FOR_BUILD} \
+   CXX=${CXX_FOR_BUILD} \
+   CXXFLAGS=${CXXFLAGS_FOR_BUILD} \
+   LDFLAGS=${LDFLAGS_FOR_BUILD} \
+   LDLIBS=${LDLIBS_FOR_BUILD} \
    "${sourceRoot}/configure" \
       --disable-api \
       --disable-gpm \