ci: map JDK vendor tokens to JvmVendorSpec constants

The CI matrix passes a short vendor token such as "eclipse" for the test
JDK toolchain. JvmVendorSpec.matching("eclipse") probes the runtime
java.vendor, which Temurin reports inconsistently across versions: JDK 8
reports "Temurin" while 11+ report "Eclipse Adoptium". A plain substring
match therefore cannot resolve a Temurin 8 toolchain, and the same gap
exists for any distribution whose vendor string differs from its token.

Map the known tokens to Gradle's built-in JvmVendorSpec constants, which
recognise every alias a distribution reports, and fall back to a
substring match for anything unmapped. Also guard against a blank vendor
so an empty token no longer narrows the toolchain query.

Mirrors pgjdbc/pgjdbc#4257, which shares this build-logic file.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: vlsi

build-logic/basics/src/main/kotlin/configureToolchain.kt

@@ -32,10 +32,27 @@ fun JavaToolchainSpec.configureToolchain(jdk: ToolchainProperties?) {
         return
     }
     languageVersion.set(JavaLanguageVersion.of(jdk.version))
-    jdk.vendor?.let {
-        vendor.set(JvmVendorSpec.matching(it))
+    jdk.vendor?.takeIf { it.isNotBlank() }?.let {
+        vendor.set(jvmVendorSpecFor(it))
     }
     if (jdk.implementation.equals("J9", ignoreCase = true)) {
         implementation.set(JvmImplementation.J9)
     }
 }
+
+// The CI matrix passes a short vendor token such as "eclipse". Map the known ones to Gradle's
+// built-in JvmVendorSpec constants, which recognise every alias a distribution reports across
+// versions; fall back to a substring match for anything unmapped. This matters for Temurin:
+// JDK 8 reports java.vendor="Temurin" while 11+ report "Eclipse Adoptium", so a plain
+// matching("eclipse") cannot resolve a Temurin 8 toolchain (JvmVendorSpec.matching probes the
+// runtime java.vendor, not the IMPLEMENTOR field of the release file).
+private fun jvmVendorSpecFor(vendor: String): JvmVendorSpec =
+    when (vendor.lowercase()) {
+        "eclipse", "adoptium", "temurin" -> JvmVendorSpec.ADOPTIUM
+        "amazon", "corretto" -> JvmVendorSpec.AMAZON
+        "azul", "zulu" -> JvmVendorSpec.AZUL
+        "bellsoft", "liberica" -> JvmVendorSpec.BELLSOFT
+        "microsoft" -> JvmVendorSpec.MICROSOFT
+        "oracle" -> JvmVendorSpec.ORACLE
+        else -> JvmVendorSpec.matching(vendor)
+    }