Add BUILD_BROKEN_DONT_CHECK_SYSTEMSDK

https://android-review.git.corp.google.com/q/topic:limit_systemsdk
introduced a new check for preventing the use of system SDKs above 34
from Java modules in the vendor partition.

As this may break some unprepared targets, introduce
BUILD_BROKEN_DONT_CHECK_SYSTEMSDK as a temporary escape hatch.

This flag will be deleted eventually.

Bug: 314011075
Test: Add BUILD_BROKEN_DONT_CHECK_SYSTEMSDK := true to BoardConfig.mk
Change-Id: Id7901f85c221bc03fa1c15ef15dbec14b783a79a

android/config.go

@@ -1849,6 +1849,10 @@ func (c *deviceConfig) BuildBrokenInputDir(name string) bool {
 	return InList(name, c.config.productVariables.BuildBrokenInputDirModules)
 }
 
+func (c *deviceConfig) BuildBrokenDontCheckSystemSdk() bool {
+	return c.config.productVariables.BuildBrokenDontCheckSystemSdk
+}
+
 func (c *config) BuildWarningBadOptionalUsesLibsAllowlist() []string {
 	return c.productVariables.BuildWarningBadOptionalUsesLibsAllowlist
 }