support/scripts/gen-bootlin-toolchains: check that toolchains exists for a certain arch

The "arches" dict lists the architectures for which Bootlin toolchains
are available, along with the corresponding Buildroot conditions for
those architecture variants.

However, there is nothing that checks that such architectures really
have Bootlin toolchains available. Even if no toolchain is available,
the architecture is considered as support, and will be listed in the
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_ARCH_SUPPORTS option, making menuconfig
believe that some Bootlin toolchain is available for the selected
architecture variant.

This is currently the case with the "mips64" architecture (as
identified by the Bootlin toolchains project). Such toolchains have
been made obsolete in toolchains.bootlin.com and replaced by the
mips64-n32 toolchains. But "mips64" is still listed in "arches",
causing this architecture to be considered as having Bootlin
toolchains available.

To avoid this to happen in the future, this commit adds a check that
verifies that an architecture listed in "arches" really has at least
one toolchain available.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 3c11e6f3c8de5482ddb36809b129179022f520a1)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/scripts/gen-bootlin-toolchains

@@ -4,6 +4,7 @@ import os.path
 import re
 import requests
 import textwrap
+import sys
 
 BASE_URL = "https://toolchains.bootlin.com/downloads/releases/toolchains"
 
@@ -479,6 +480,10 @@ def get_toolchains():
                 version = parts[2][len("bleeding-edge-"):]
             tmp[(arch, libc, variant)] = version
 
+        if len(tmp) == 0:
+            print("ERROR: no toolchains found for architecture %s" % arch)
+            sys.exit(1)
+
         toolchains += [Toolchain(k[0], k[1], k[2], v) for k, v in tmp.items()]
 
     return toolchains