gcc-clang-compatibility: Add support for gcc-toolset installations

clang may use a gcc from gcc-toolset instead the system version. In that
case we need to test the compatibility with that one, not with the
system based gcc.

gcc-clang-compatibility/test.sh

@@ -2,14 +2,25 @@
 
 tmp=$(mktemp -d)
 
+# clang not necessarily depends on system gcc. It might depend on gcc from
+# gcc-toolset-XX, in such case we need to test the compatibility with that one.
+# We can get that from `clang -v` output.
+TOOLSET=$(clang -v |& grep "Selected GCC installation" | grep -P -o '(dev|gcc-)toolset-[0-9]*') ||:
+if [[ "x" = "x${TOOLSET}" ]]; then
+    GCC="g++"
+else
+    GCC="scl enable ${TOOLSET} -- g++"
+    echo "Testing with g++ from ${TOOLSET}"
+fi
+
 # Build the source with GCC, link it with clang
-g++ -c hello.cpp -o ${tmp}/hello.o
+${GCC} -c hello.cpp -o ${tmp}/hello.o
 clang++ -o ${tmp}/hello ${tmp}/hello.o
 ${tmp}/hello | grep "Hello world"
 rm -rf ${tmp}/*
 
 # Build the source with clang, link it with GCC
 clang++ -c hello.cpp -o ${tmp}/hello.o
-g++ -o ${tmp}/hello ${tmp}/hello.o
+${GCC} -o ${tmp}/hello ${tmp}/hello.o
 ${tmp}/hello | grep "Hello world"
 rm -rf ${tmp}/*