Flip --incompatible_disable_legacy_crosstool_fields and --incompatibl…

…e_disable_expand_if_all_available_in_flag_set

Fixes #7008
Fixes #6861

This is an encore of c18be0b.

TESTED=https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/852#5c90f69e-c5d2-44c1-8067-0bde4cba6f6d (remote execution is fixed after syncing, verified locally)

RELNOTES: `--incompatible_disable_legacy_crosstool_fields` has been flipped (#6861)
`--incompatible_disable_expand_if_all_available_in_flag_set` has been flipped (#7008)
PiperOrigin-RevId: 239567807

src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java

@@ -710,7 +710,7 @@ public Label getFdoPrefetchHintsLabel() {
   @Option(
       name = "incompatible_disable_legacy_crosstool_fields",
       oldName = "experimental_disable_legacy_crosstool_fields",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
       metadataTags = {
@@ -753,7 +753,7 @@ public Label getFdoPrefetchHintsLabel() {
 
   @Option(
       name = "incompatible_disable_expand_if_all_available_in_flag_set",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
       metadataTags = {