gcc/7.3.0

Use tar.gz source instead of bz2, because that's what gnu provides

Programming/gcc/7/variants

@@ -1,2 +1,3 @@
 gcc/7.1.0	stable		b:gmp/6.1.2 b:mpfr/3.1.5 b:mpc/1.0.3
 gcc/7.2.0	stable		b:gmp/6.1.2 b:mpfr/3.1.5 b:mpc/1.0.3-2
+gcc/7.3.0	stable		b:gmp/6.1.2 b:mpfr/4.0.0 b:mpc/1.1.0

Programming/gcc/build

@@ -1,6 +1,6 @@
 #!/usr/bin/env modbuild
 
-SOURCE_URL="https://ftp.gnu.org/gnu/gcc/$P-$V/$P-$V.tar.bz2"
+SOURCE_URL="https://ftp.gnu.org/gnu/gcc/$P-$V/$P-$V.tar.gz"
 
 pbuild::patch_sources_Darwin() {
 	if (( V_MAJOR == 4 && V_MINOR <= 8 )) || \