toolchain/helpers.mk: perform reverse support checks

Previously, it was possible for external toolchains to be used that had
support for languages or libraries that Buildroot was not aware of.

If Buildroot is not made aware of this support, it will not know to copy
the requisite libraries into the filesystem.

This is problematic as packages may perform their own checks [0] to find
out what the toolchain supports and builds will link against libraries
from the toolchain but will be missing dependencies in the filesystem.

Now, the support helpers alert the user when a toolchain supports a
language or library that has not been set in the Buildroot configuration.

Also, while we're here, add `-ffree-form` to the Fortran check to
suppress a meaningless warning.

[0]: https://bugs.busybox.net/show_bug.cgi?id=15634

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

toolchain/helpers.mk

@@ -343,11 +343,14 @@ check_arm_abi = \
 #
 check_cplusplus = \
 	__CROSS_CXX=$(strip $1) ; \
-	$${__CROSS_CXX} -v > /dev/null 2>&1 ; \
-	if test $$? -ne 0 ; then \
+	__HAS_CXX=`$${__CROSS_CXX} -v > /dev/null 2>&1 && echo y`; \
+	if [ "$${__HAS_CXX}" != "y" -a "$(BR2_INSTALL_LIBSTDCPP)" = y ] ; then \
 		echo "C++ support is selected but is not available in external toolchain" ; \
 		exit 1 ; \
-	fi
+	elif [ "$${__HAS_CXX}" = "y" -a "$(BR2_INSTALL_LIBSTDCPP)" != y ] ; then \
+		echo "C++ support is not selected but is available in external toolchain" ; \
+		exit 1 ; \
+	fi \
 
 #
 #
@@ -358,14 +361,16 @@ check_cplusplus = \
 check_dlang = \
 	__CROSS_GDC=$(strip $1) ; \
 	__o=$(BUILD_DIR)/.br-toolchain-test-dlang.tmp ; \
-	printf 'import std.stdio;\nvoid main() { writeln("Hello World!"); }\n' | \
-	$${__CROSS_GDC} -x d -o $${__o} - ; \
-	if test $$? -ne 0 ; then \
-		rm -f $${__o}* ; \
+	__HAS_DLANG=`printf 'import std.stdio;\nvoid main() { writeln("Hello World!"); }\n' | \
+		$${__CROSS_GDC} -x d -o $${__o} - >/dev/null 2>&1 && echo y`; \
+	rm -f $${__o}* ; \
+	if [ "$${__HAS_DLANG}" != "y" -a "$(BR2_TOOLCHAIN_HAS_DLANG)" = y ] ; then \
 		echo "D language support is selected but is not available in external toolchain" ; \
 		exit 1 ; \
-	fi ; \
-	rm -f $${__o}* \
+	elif [ "$${__HAS_DLANG}" = "y" -a "$(BR2_TOOLCHAIN_HAS_DLANG)" != y ] ; then \
+		echo "D language support is not selected but is available in external toolchain" ; \
+		exit 1 ; \
+	fi \
 
 #
 #
@@ -376,14 +381,16 @@ check_dlang = \
 check_fortran = \
 	__CROSS_FC=$(strip $1) ; \
 	__o=$(BUILD_DIR)/.br-toolchain-test-fortran.tmp ; \
-	printf 'program hello\n\tprint *, "Hello Fortran!\\n"\nend program hello\n' | \
-	$${__CROSS_FC} -x f95 -o $${__o} - ; \
-	if test $$? -ne 0 ; then \
-		rm -f $${__o}* ; \
+	__HAS_FORTRAN=`printf 'program hello\n\tprint *, "Hello Fortran!\\\n"\nend program hello\n' | \
+		$${__CROSS_FC} -x f95 -ffree-form -o $${__o} - && echo y`; \
+	rm -f $${__o}* ; \
+	if [ "$${__HAS_FORTRAN}" != "y" -a "$(BR2_TOOLCHAIN_HAS_FORTRAN)" = y ] ; then \
 		echo "Fortran support is selected but is not available in external toolchain" ; \
 		exit 1 ; \
-	fi ; \
-	rm -f $${__o}* \
+	elif [ "$${__HAS_FORTRAN}" = "y" -a "$(BR2_TOOLCHAIN_HAS_FORTRAN)" != y ] ; then \
+		echo "Fortran support is not selected but is available in external toolchain" ; \
+		exit 1 ; \
+	fi \
 
 #
 #
@@ -394,14 +401,16 @@ check_fortran = \
 check_openmp = \
 	__CROSS_CC=$(strip $1) ; \
 	__o=$(BUILD_DIR)/.br-toolchain-test-openmp.tmp ; \
-	printf '\#include <omp.h>\nint main(void) { return omp_get_thread_num(); }' | \
-	$${__CROSS_CC} -fopenmp -x c -o $${__o} - ; \
-	if test $$? -ne 0 ; then \
-		rm -f $${__o}* ; \
+	__HAS_OPENMP=`printf '\#include <omp.h>\nint main(void) { return omp_get_thread_num(); }' | \
+		$${__CROSS_CC} -fopenmp -x c -o $${__o} - >/dev/null 2>&1 && echo y` ; \
+	rm -f $${__o}* ; \
+	if [ "$${__HAS_OPENMP}" != "y" -a "$(BR2_TOOLCHAIN_HAS_OPENMP)" = y ] ; then \
 		echo "OpenMP support is selected but is not available in external toolchain"; \
 		exit 1 ; \
-	fi ; \
-	rm -f $${__o}* \
+	elif [ "$${__HAS_OPENMP}" = "y" -a "$(BR2_TOOLCHAIN_HAS_OPENMP)" != y ] ; then \
+		echo "OpenMP support is not selected but is available in external toolchain"; \
+		exit 1 ; \
+	fi \
 
 #
 # Check that the cross-compiler given in the configuration exists