rtl-unification: remove dead archive-resolution code; last test off the archive

Partial Stage-3 teardown — the safe removals that do not affect the bootstrap
chain (the runtime Makefile/ar stay until a release ships a source-build-capable
binary, since the v0.12.0-rooted rolling-bootstrap replay needs them for its
pre-source-build commits):

- Remove FindRTLArchive + TToolchain.RTLPath from uToolchain — dead since the
  link paths source-build the RTL; the field was set but never read.
- TInternalLinkerE2ETests gated on blaise_rtl.a existing, so it silently skipped
  once the archive was gone; gate on the RTL source instead.  It now runs (5
  tests) — the last automated test still tied to the archive.
- Refresh the runtime mem test/bench build-instruction comments to the
  source-built, archive-free invocation (blaise --output, no qbe+gcc+.a).

Full suite green (3829 tests, 1 ignored) — TInternalLinkerE2ETests no longer
skipped.

compiler/src/main/pascal/uToolchain.pas

@@ -50,7 +50,6 @@ type
     QBE:        TTool;   { QBE backend only }
     Assembler:  TTool;   { native backend: assemble .s -> .o (reserved) }
     Linker:     TTool;   { both backends: link final binary }
-    RTLPath:    string;  { '' if not found }
   end;
 
   { One external tool a backend declares it needs (TBackendDriver.DescribeTools).
@@ -87,7 +86,6 @@ function ResolveToolchain(const ATarget: TTargetDesc): TToolchain;
 function ResolveQBE: TTool;
 function ResolveAssembler: TTool;
 function ResolveLinker(const ATarget: TTargetDesc): TTool;
-function FindRTLArchive(const ATarget: TTargetDesc): string;
 
 { Directory containing the running compiler binary (ParamStr(0)). }
 function CompilerBinDir: string;
@@ -363,18 +361,6 @@ begin
     + '../src/main/pascal');
 end;
 
-function FindRTLArchive(const ATarget: TTargetDesc): string;
-var
-  BinDir: string;
-begin
-  Result := GetEnvironmentVariable('BLAISE_RTL');
-  if (Result <> '') and FileExists(Result) then Exit;
-  BinDir := CompilerBinDir();
-  Result := IncludeTrailingPathDelimiter(BinDir) + 'blaise_rtl.a';
-  if FileExists(Result) then Exit;
-  Result := '';
-end;
-
 { ------------------------------------------------------------------ }
 { Top-level resolver                                                   }
 { ------------------------------------------------------------------ }
@@ -384,7 +370,6 @@ begin
   Result.QBE       := ResolveQBE();
   Result.Assembler := ResolveAssembler();
   Result.Linker    := ResolveLinker(ATarget);
-  Result.RTLPath   := FindRTLArchive(ATarget);
 end;
 
 end.

compiler/src/test/pascal/cp.test.linker.pas

@@ -1299,13 +1299,15 @@ end;
 
 function TInternalLinkerE2ETests.CompilerAvailable: Boolean;
 begin
+  { The compiler source-builds the RTL itself (no blaise_rtl.a); only the binary
+    and the RTL source need to be present. }
   Result := FileExists(FCompiler) and
-            FileExists(ProjectRoot() + 'compiler/target/blaise_rtl.a');
+            FileExists(FRTLPath + '/runtime.arc.pas');
   if (not Result) and (not GIntLinkSkipNoted) then
   begin
     GIntLinkSkipNoted := True;
     WriteLn(StdErr, 'note: TInternalLinkerE2ETests skipped — compiler binary "',
-            FCompiler, '" not found');
+            FCompiler, '" or RTL source not found');
   end;
 end;
 

runtime/src/test/pascal/bench_blaise_mem.pas

@@ -22,12 +22,10 @@
   Output: elapsed time in milliseconds per workload.  Compare across
   runs to detect regressions or improvements.
 
-  Build:
+  Build (the compiler source-builds and links the RTL — no blaise_rtl.a):
     blaise --source runtime/src/test/pascal/bench_blaise_mem.pas \
-           --unit-path runtime/src/main/pascal \
-           --emit-ir > /tmp/bench_mem.ssa
-    vendor/qbe/qbe -o /tmp/bench_mem.s /tmp/bench_mem.ssa
-    gcc -o /tmp/bench_mem /tmp/bench_mem.s compiler/target/blaise_rtl.a
+           --unit-path compiler/src/main/pascal \
+           --output /tmp/bench_mem
     /tmp/bench_mem
 }
 

runtime/src/test/pascal/test_blaise_mem.pas

@@ -12,13 +12,11 @@
   the string and ARC subsystems.  punit is the correct framework here
   because blaise_mem has zero dependency on stdlib or ARC.
 
-  Build:
+  Build (the compiler source-builds and links the RTL — no blaise_rtl.a):
     blaise --source runtime/src/test/pascal/test_blaise_mem.pas \
-           --unit-path runtime/src/main/pascal \
+           --unit-path compiler/src/main/pascal \
            --unit-path runtime/src/test/pascal \
-           --emit-ir > /tmp/test_mem.ssa
-    vendor/qbe/qbe -o /tmp/test_mem.s /tmp/test_mem.ssa
-    gcc -o /tmp/test_mem /tmp/test_mem.s compiler/target/blaise_rtl.a
+           --output /tmp/test_mem
     /tmp/test_mem -v
 }