compiler: pass large aggregates by pointer

LLVM ComputeValueVTs recursively expands arrays and structs into one
value type per scalar leaf. SelectionDAG call lowering allocates data
structures proportional to this count, which makes very large values
exhaust memory or crash LLVM.

Count scalar leaves and use pointers for internal parameters and results
when the count exceeds 1024. A result pointer is the first parameter,
and aggregate parameters point to read-only memory. Exported function
types are unchanged.

Keep these SSA values in memory and copy them with memcpy when needed.
Handle calls, interfaces, maps, channels, selects, defers, goroutines,
phis, and multiple results. Update the expected compiler IR and re-enable
the native compress/flate tests.

GNUmakefile

@@ -387,9 +387,7 @@ TEST_PACKAGES_FAST = \
 
 # archive/zip requires os.ReadAt, which is not yet supported on windows
 # bytes requires mmap
-# compress/flate appears to hang on wasi; on all targets Go 1.27's new
-#   compress/flate.indexTokens returns a ~262KB struct by value which crashes
-#   LLVM's X86 instruction selector during LTO codegen
+# compress/flate appears to hang on wasi
 # crypto/aes needs reflect.Type.Method(), not yet implemented
 # crypto/des fails on wasi, needs panic()/recover()
 # crypto/hmac fails on wasi, it exits with a "slice out of range" panic
@@ -411,6 +409,7 @@ TEST_PACKAGES_FAST = \
 # Additional standard library packages that pass tests on individual platforms
 TEST_PACKAGES_LINUX := \
 	archive/zip \
+	compress/flate \
 	context \
 	crypto/aes \
 	crypto/des \
@@ -438,6 +437,7 @@ TEST_PACKAGES_DARWIN := $(TEST_PACKAGES_LINUX)
 
 # os/user requires t.Skip() support
 TEST_PACKAGES_WINDOWS := \
+	compress/flate \
 	crypto/des \
 	crypto/hmac \
 	image \