Handle zstd not being present on Android.

CMakeLists.txt

@@ -225,10 +225,17 @@ set(REQUIRED_LIBS
  capnp
 # zlib is required to handle ELF compression
  zlib
-# zstd is required to handle ELF compression
- libzstd
 )
 
+if(NOT ANDROID)
+ set(REQUIRED_LIBS
+ ${REQUIRED_LIBS}
+ # zstd is required to handle ELF compression, but isn't available on Android.
+ libzstd
+ )
+ add_definitions(-DZSTD=1)
+endif()
+
 foreach(required_lib ${REQUIRED_LIBS})
  string(TOUPPER ${required_lib} PKG)
  if(NOT SKIP_PKGCONFIG)
@@ -715,10 +722,13 @@ endif()
 target_link_libraries(rr
  ${CMAKE_DL_LIBS}
  ${ZLIB_LDFLAGS}
- ${LIBZSTD_LDFLAGS}
  brotli
 )
 
+if(NOT ANDROID)
+ target_link_libraries(rr ${LIBZSTD_LDFLAGS})
+endif()
+
 if(staticlibs)
  # Urgh ... this might not work for everyone, but there doesn't seem to be
  # a way to persuade pkg-confing/pkg_check_modules to produce the right flags

src/ElfReader.cc

@@ -7,7 +7,9 @@
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <zlib.h>
+#ifdef ZSTD
 #include <zstd.h>
+#endif
 
 #include "log.h"
 #include "util.h"
@@ -238,13 +240,15 @@ const vector<uint8_t>* ElfReaderImpl<Arch>::decompress_section(SectionOffsets of
  FATAL() << "inflateEnd failed!";
  return nullptr;
  }
+#ifdef ZSTD
  } else if (zstd) {
  size_t compressed_size = offsets.end - offsets.start;
  size_t size = ZSTD_decompress(&v->front(), v->size(),
  r.read_bytes(offsets.start, compressed_size), compressed_size);
  if (size != v->size()) {
  FATAL() << "zstd decompression failed";
  }
+#endif
  } else {
  FATAL() << "Unrecognized compression algorithm";
  }