libarchive: fix harness and improve build setup (#12052)

This fixes a major harness issue in the `libarchive` fuzzer and resolves
a fuzzing roadblock issue related to the build setup.
All calls after `archive_read_add_passphrase` currently exit early
because the decoder state is marked as invalid due to incorrect API
usage.

When combined with libarchive/libarchive#2229,
this should improve coverage from ~15% to >45%.
While the harness issue
[regressed](#9452 (comment))
at some point, it seems like the CRC build flag issue was always present
in oss-fuzz's libarchive setup.

Thanks!

projects/libarchive/build.sh

@@ -27,12 +27,9 @@ DEPS=/deps
 
 cd $SRC/libarchive
 
-sed -i 's/-Wall//g' ./CMakeLists.txt
-sed -i 's/-Werror//g' ./CMakeLists.txt
-
 mkdir build2
 cd build2
-cmake -DCHECK_CRC_ON_SOLID_SKIP=1 -DDONT_FAIL_ON_CRC_ERROR=1 ../
+cmake -DDONT_FAIL_ON_CRC_ERROR=ON -DENABLE_WERROR=OFF ../
 make -j$(nproc)
 
 # build seed

projects/libarchive/libarchive_fuzzer.cc

@@ -33,13 +33,13 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
     return 0;
   }
 
+  archive_read_add_passphrase(a, "secret");
+
   if (ARCHIVE_OK != archive_read_open_memory(a, buf, len)) {
     archive_read_free(a);
     return 0;
   }
 
-  archive_read_add_passphrase(a, "secret");
-
   while(1) {
     std::vector<uint8_t> data_buffer(getpagesize(), 0);
     struct archive_entry *entry;