pmbootstrap aportgen gcc{,4,6}*: fix depends

Explicitly depend on mpc1, mpfr3. Our generated gcc aports use the
!tracedeps option, so we need to explicitly set the libraries it
depends on.

This has mostly not been an issue, as we are installing our gcc
packages together with Alpine's gcc package, which causes the libraries
to get installed anyway.

Related: pmaports#236

pmb/aportgen/gcc.py

@@ -45,7 +45,7 @@ def generate(args, pkgname):
         "pkgname": pkgname,
         "pkgdesc": "Stage2 cross-compiler for " + arch,
         "arch": "x86_64",
-        "depends": "isl binutils-" + arch,
+        "depends": "isl binutils-" + arch + " mpc1 mpfr3",
         "makedepends_build": "gcc g++ paxmark bison flex texinfo gawk zip gmp-dev mpfr-dev mpc1-dev zlib-dev",
         "makedepends_host": "linux-headers gmp-dev mpfr-dev mpc1-dev isl-dev zlib-dev musl-dev-" + arch + " binutils-" + arch,
         "subpackages": "g++-" + arch + ":gpp" if prefix == "gcc" else "",