sys-devel/gsl: respect CC and flags

Closes: https://bugs.gentoo.org/847328
Signed-off-by: Alessandro Barbieri <lssndrbarbieri@gmail.com>

sys-devel/gsl/files/gsl-4.1.5-respect-flags.patch

@@ -0,0 +1,13 @@
+--- a/src/c
++++ b/src/c
+@@ -156,8 +156,8 @@
+ #
+ case "$($CCNAME --version)" in
+ *gcc*|*GCC*)
+-    [ -z "$BOOM_MODEL_NOOPT" ] && CCDEBUG="-O2"
+-    [ -z "$BOOM_MODEL_NOOPT" ] && CCNODEBUG="$CCNODEBUG -O2"
++    [ -z "$BOOM_MODEL_NOOPT" ] && CCDEBUG="${CFLAGS}"
++    [ -z "$BOOM_MODEL_NOOPT" ] && CCNODEBUG="$CCNODEBUG ${CFLAGS}"
+     CCOPTS="-D_REENTRANT -D_GNU_SOURCE -Wall -Wno-unused -fno-strict-aliasing"
+     #  We assume the following standard libraries are all present.
+     #  If your build is failing because of missing libraries then

sys-devel/gsl/gsl-4.1.5-r1.ebuild

@@ -3,6 +3,8 @@
 
 EAPI=8
 
+inherit toolchain-funcs
+
 DESCRIPTION='iMatix GSL code generator'
 HOMEPAGE="https://github.com/zeromq/gsl"
 SRC_URI="https://github.com/zeromq/${PN}/archive/refs/tags/v${PV}.tar.gz -> ${P}.tar.gz"
@@ -15,6 +17,15 @@ IUSE="examples"
 DEPEND="dev-libs/libpcre:3"
 RDEPEND="${DEPEND}"
 
+PATCHES=( "${FILESDIR}/${P}-respect-flags.patch" )
+
+src_prepare() {
+	tc-export RANLIB
+	export CCNAME="$(tc-getCC)"
+	export CCPLUS="$(tc-getCXX)"
+	default
+}
+
 src_install() {
 	DESTDIR="${D}/usr" emake install
 	if use examples; then