surrealdb: use nightly Rust (#11777)

The rust-lang/rust#110475 issue referenced is no longer a problem since
the `geo` crate has been updated in SurrealDB. However, the change in
default Rust version in the image builder implemented in
#11681 breaks fuzzing due to SurrealDB now requiring Rust
1.77 after surrealdb/surrealdb#3591, leading to
a bump in the MSRV in surrealdb/surrealdb#3778.

I have replaced the obsolete `--cfg uuid_unstable` for the generic
`--cfg surrealdb_unstable`, which will allow fuzzing any features still
deemed unstable in SurrealDB including the new experimental parser.

projects/surrealdb/Dockerfile

@@ -18,10 +18,10 @@ FROM gcr.io/oss-fuzz-base/base-builder-rust
 RUN git clone --depth 1 https://github.com/surrealdb/surrealdb surrealdb
 RUN git clone --depth 1 https://github.com/surrealdb/docs.surrealdb.com.git surrealdb_website
 WORKDIR surrealdb
-# TODO(surrealdb/surrealdb#1873): Remove `RUN rustup.*` lines once 
-# rust-lang/rust#110475 is fixed.
-RUN rustup install nightly-2023-04-21
-RUN rustup default nightly-2023-04-21
+# TODO(gguillemas): Remove `RUN rustup.*` lines once
+# google/oss-fuzz#11681 is reverted to use nightly in image builder.
+RUN rustup install nightly
+RUN rustup default nightly
 # needed for MSAN and coverage build
 RUN rustup component add rust-src
 COPY build.sh $SRC/

projects/surrealdb/build.sh

@@ -20,7 +20,7 @@ cd lib
 cp fuzz/fuzz_targets/*.dict $OUT/ || true
 
 # Add additional compiler flags required for a successful build.
-export RUSTFLAGS="$RUSTFLAGS --cfg uuid_unstable"
+export RUSTFLAGS="$RUSTFLAGS --cfg surrealdb_unstable"
 
 cargo fuzz build -O --debug-assertions