util/xcompile: Look for the host compiler in XGCCPATH, too (and first)

If there's a host compiler in XGCCPATH, it's likely the same
relatively-current version we use for coreboot, and it's a well-known
quantity, so let's prefer that over alternatives by default.

In addition, look for the C++ host compiler as well.

Change-Id: If50341df169a476899b5a5ffd4c4fb6d21c3f4ac
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43144
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/xcompile/xcompile

@@ -56,7 +56,9 @@ elif [ "$(iasl 2>/dev/null | grep -c ACPI)" -gt 0 ]; then
 	IASL=iasl
 fi
 
-if program_exists gcc; then
+if program_exists "${XGCCPATH}/gcc"; then
+	HOSTCC="${XGCCPATH}/gcc"
+elif program_exists gcc; then
 	HOSTCC=gcc
 elif program_exists cc; then
 	HOSTCC=cc
@@ -64,6 +66,20 @@ else
 	die "no host compiler found"
 fi
 
+# Look for a C++ compiler (for kconfig's qconf), but don't fail if there is
+# none, just set the compiler to false(1) which will break early enough if
+# used while being less confusing than errors about "g not found" when
+# "$HOSTCXX -g" evaluates to "-g" and make drops the leading dash.
+if program_exists "${XGCCPATH}/g++"; then
+	HOSTCXX="${XGCCPATH}/g++"
+elif program_exists g++; then
+	HOSTCXX=g++
+elif program_exists c++; then
+	HOSTCXX=c++
+else
+	HOSTCXX=false
+fi
+
 # try to find the core count using various methods
 CORES="$(getconf _NPROCESSORS_ONLN 2>/dev/null)"
 if [ -z "$CORES" ]; then
@@ -87,6 +103,7 @@ cat <<EOF
 XGCCPATH:=${XGCCPATH}
 IASL:=${IASL}
 HOSTCC?=${HOSTCC}
+HOSTCXX?=${HOSTCXX}
 CPUS?=${CORES}
 
 EOF