avr_gcc: fix LIBRARY_PATH conflict

* gcc tries to set this to the target libs, but haiku use it for the
runtime_loader
* We have a workaround in our target config, but it is not used when
building a cross compiler with a non-haiku target
* Apply the workaround manually by forcing LIBRARY_PATH_ENV

sys-devel/avr_gcc/avr_gcc-4.8.2_2014_03_20.recipe

@@ -39,6 +39,7 @@ PROVIDES="
 REQUIRES="
 	haiku$secondaryArchSuffix >= $haikuVersion
 	cmd:avr_as$secondaryArchSuffix
+	lib:libstdc++$secondaryArchSuffix
 	"
 BUILD_REQUIRES="
 	cmd:avr_as$secondaryArchSuffix
@@ -47,6 +48,7 @@ BUILD_PREREQUIRES="
 	haiku${secondaryArchSuffix}_devel >= $haikuVersion
 	cmd:autoconf
 	cmd:awk
+	cmd:bison
 	cmd:find
 	cmd:flex
 	cmd:gcc$secondaryArchSuffix
@@ -79,7 +81,11 @@ BUILD()
 	mkdir -p $objectsDir
 	cd $objectsDir
 
-	CFLAGS="-O2 -U_FORTIFY_SOURCE" CXXFLAGS="-O2" "$sourceDir/configure" \
+	# Setting a quoted string in an environment variable is ugly.
+	echo '#define LIBRARY_PATH_ENV "AVR_LIBRARY_PATH"' > haiku_host.h
+
+	CXXFLAGS="-O2 -include $objectsDir/haiku_host.h" \
+	CFLAGS="-O2 -U_FORTIFY_SOURCE" "$sourceDir/configure" \
 		--build=$effectiveTargetMachineTriple \
 		--prefix=$installDir --libexecdir=$installDir/lib --mandir=$manDir \
 		--docdir=$docDir --disable-nls --disable-libssp --with-gnu-ld \