Ports/gcc: Install dependencies as ports

This lets us remove a couple manual config.sub patches.

Ports/gcc/package.sh

@@ -6,12 +6,9 @@ configopts=("--target=${SERENITY_ARCH}-pc-serenity" "--with-sysroot=/" "--with-b
 files="https://ftpmirror.gnu.org/gnu/gcc/gcc-${version}/gcc-${version}.tar.xz gcc-${version}.tar.xz d08edc536b54c372a1010ff6619dd274c0f1603aa49212ba20f7aa2cda36fa8b"
 makeopts=("all-gcc" "all-target-libgcc" "all-target-libstdc++-v3" "-j$(nproc)")
 installopts=("DESTDIR=${SERENITY_INSTALL_ROOT}" "install-gcc" "install-target-libgcc" "install-target-libstdc++-v3")
-depends=("binutils")
+depends=("binutils" "gmp" "mpfr" "mpc" "isl")
 auth_type="sha256"
 
-post_fetch() {
-    run contrib/download_prerequisites
-}
 
 build() {
     run make "${makeopts[@]}"

Ports/gcc/patches/dependencies-config.patch

@@ -1,44 +0,0 @@
-diff -ru gcc/isl/config.sub gcc-patched/isl/config.sub
---- gcc/isl/config.sub	2016-01-24 21:50:53.000000000 +0100
-+++ gcc-patched/isl/config.sub	2019-05-28 16:34:43.396758421 +0200
-@@ -1361,6 +1361,7 @@
- 	# Each alternative MUST END IN A *, to match a version number.
- 	# -sysv* is not here because it comes later, after sysvr4.
- 	-gnu* | -bsd* | -mach* | -minix* | -genix* | -ultrix* | -irix* \
-+	      | -serenity* \
- 	      | -*vms* | -sco* | -esix* | -isc* | -aix* | -cnk* | -sunos | -sunos[34]*\
- 	      | -hpux* | -unos* | -osf* | -luna* | -dgux* | -auroraux* | -solaris* \
- 	      | -sym* | -kopensolaris* | -plan9* \
-diff -ru gcc/mpc/config.sub gcc-patched/mpc/config.sub
---- gcc/mpc/config.sub	2015-02-16 13:28:25.000000000 +0100
-+++ gcc-patched/mpc/config.sub	2019-05-28 16:34:22.308458127 +0200
-@@ -1369,6 +1369,7 @@
- 	# Each alternative MUST END IN A *, to match a version number.
- 	# -sysv* is not here because it comes later, after sysvr4.
- 	-gnu* | -bsd* | -mach* | -minix* | -genix* | -ultrix* | -irix* \
-+	      | -serenity* \
- 	      | -*vms* | -sco* | -esix* | -isc* | -aix* | -cnk* | -sunos | -sunos[34]*\
- 	      | -hpux* | -unos* | -osf* | -luna* | -dgux* | -auroraux* | -solaris* \
- 	      | -sym* | -kopensolaris* | -plan9* \
-diff -ru gcc/mpfr/config.sub gcc-patched/mpfr/config.sub
---- gcc/mpfr/config.sub	2016-03-06 12:33:18.000000000 +0100
-+++ gcc-patched/mpfr/config.sub	2019-05-28 16:34:33.052611048 +0200
-@@ -1375,6 +1375,7 @@
- 	# Each alternative MUST END IN A *, to match a version number.
- 	# -sysv* is not here because it comes later, after sysvr4.
- 	-gnu* | -bsd* | -mach* | -minix* | -genix* | -ultrix* | -irix* \
-+	      | -serenity* \
- 	      | -*vms* | -sco* | -esix* | -isc* | -aix* | -cnk* | -sunos | -sunos[34]*\
- 	      | -hpux* | -unos* | -osf* | -luna* | -dgux* | -auroraux* | -solaris* \
- 	      | -sym* | -kopensolaris* | -plan9* \
-diff -ru gcc/gmp/configfsf.sub gcc-patched/gmp/configfsf.sub
---- gcc/gmp/configfsf.sub	2015-11-01 16:19:48.000000000 +0100
-+++ gcc-patched/gmp/configfsf.sub	2019-05-28 16:47:14.095698619 +0200
-@@ -1375,6 +1375,7 @@
- 	# Each alternative MUST END IN A *, to match a version number.
- 	# -sysv* is not here because it comes later, after sysvr4.
- 	-gnu* | -bsd* | -mach* | -minix* | -genix* | -ultrix* | -irix* \
-+	      | -serenity* \
- 	      | -*vms* | -sco* | -esix* | -isc* | -aix* | -cnk* | -sunos | -sunos[34]*\
- 	      | -hpux* | -unos* | -osf* | -luna* | -dgux* | -auroraux* | -solaris* \
- 	      | -sym* | -kopensolaris* | -plan9* \