Re-disable bootstrap (#4380)

Bootstrap gets confused because gcc changes thorugh build.
Not sure why this happens, but the compiled gcc seems to work
just fine.

(This is the version working on my setup. Re-enabling bootstrap was only a test which I accidentally uploaded.)

packages/gcc10.rb

@@ -58,6 +58,7 @@ class Gcc10 < Package
         "--disable-multilib",
         "--enable-lto",
         "--enable-threads=posix",
+        "--disable-bootstrap",
         "--disable-werror",
         "--disable-libmpx",
         "--enable-static",
@@ -78,6 +79,7 @@ class Gcc10 < Package
         "--enable-lto",
         "--disable-multilib",
         "--enable-threads=posix",
+        "--disable-bootstrap",
         "--disable-werror",
         "--disable-libmpx",
         "--enable-static",
@@ -95,6 +97,7 @@ class Gcc10 < Package
         "--enable-lto",
         "--disable-multilib",
         "--enable-threads=posix",
+        "--disable-bootstrap",
         "--disable-werror",
         "--disable-libmpx",
         "--enable-static",