[libFuzzer] Re-enable libFuzzer on i386 Linux and fix test

[metzman]

Summary

Re-enable libFuzzer on i386 Linux after it was accidentally
disabled.

Also disable gc-sections.test on i386 since lld isn't
garbage collecting properly with ASAN on i386.

[metzman]

Please take a look.
This reenables libFuzzer on i386 on Linux (accidentally disabled here), and fixes a previously failing test.

[morehouse]

LGTM

cmake/config-ix.cmake

 endif()
 
 set(ALL_SANITIZER_COMMON_SUPPORTED_ARCH ${X86} ${X86_64} ${PPC64}
     ${ARM32} ${ARM64} ${MIPS32} ${MIPS64} ${S390X})
 set(ALL_ASAN_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64}
     ${MIPS32} ${MIPS64} ${PPC64} ${S390X})
 set(ALL_CRT_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64})
 set(ALL_DFSAN_SUPPORTED_ARCH ${X86_64} ${MIPS64} ${ARM64})
-if(LINUX)
+
+if(ANDROID)
+  set(OS_NAME "Android")
+else()
+  set(OS_NAME "${CMAKE_SYSTEM_NAME}")
+endif()
+
+if(OS_NAME MATCHES "Linux")
   set(ALL_FUZZER_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM64})
 else()
   set(ALL_FUZZER_SUPPORTED_ARCH ${X86_64} ${ARM64})
 endif()
 
 if(APPLE)
   set(ALL_LSAN_SUPPORTED_ARCH ${X86} ${X86_64} ${MIPS64} ${ARM64})
 else()

 
 find_program(GOLD_EXECUTABLE NAMES ${LLVM_DEFAULT_TARGET_TRIPLE}-ld.gold ld.gold ${LLVM_DEFAULT_TARGET_TRIPLE}-ld ld DOC "The gold linker")
 
 if(COMPILER_RT_SUPPORTED_ARCH)
   list(REMOVE_DUPLICATES COMPILER_RT_SUPPORTED_ARCH)
 endif()
 message(STATUS "Compiler-RT supported architectures: ${COMPILER_RT_SUPPORTED_ARCH}")
 
-if(ANDROID)
-  set(OS_NAME "Android")
-else()
-  set(OS_NAME "${CMAKE_SYSTEM_NAME}")
-endif()
-
 set(ALL_SANITIZERS asan;dfsan;msan;hwasan;tsan;safestack;cfi;scudo;ubsan_minimal)
 set(COMPILER_RT_SANITIZERS_TO_BUILD all CACHE STRING
     "sanitizers to build if supported on the target (all;${ALL_SANITIZERS})")
 list_replace(COMPILER_RT_SANITIZERS_TO_BUILD all "${ALL_SANITIZERS}")
 
 if (SANITIZER_COMMON_SUPPORTED_ARCH AND NOT LLVM_USE_SANITIZER AND
     (OS_NAME MATCHES "Android|Darwin|Linux|FreeBSD|NetBSD|OpenBSD|Fuchsia|SunOS" OR
     (OS_NAME MATCHES "Windows" AND NOT CYGWIN AND

test/fuzzer/gc-sections.test

 REQUIRES: linux, lld-available
+# LLD isn't pruning functions as we expect it to with ASAN on i386.
+UNSUPPORTED: i386
 
 No gc-sections:
 RUN: %cpp_compiler %S/GcSectionsTest.cpp -o %t
 RUN: nm %t | grep UnusedFunctionShouldBeRemovedByLinker | count 1
 
 With gc-sections. Currently, we can't remove unused code except with LLD.
 RUN: %cpp_compiler %S/GcSectionsTest.cpp -o %t -fuse-ld=lld -ffunction-sections -Wl,-gc-sections
 RUN: nm %t | not grep UnusedFunctionShouldBeRemovedByLinker
 RUN: %run %t -runs=0 2>&1 | FileCheck %s
 
 CHECK-NOT: ERROR: The size of coverage PC tables does not match