Upgrade ios min version to 8

[kubamracek]

Summary

Version 8 is the first version to support the __thread
keyword, which is required for building lsan for
64-bit ios.

[kubamracek]

I am in favor of this change (I wanted to raise the deployment target to 8.0 for some time already). @kcc do you still need sanitizers to support deploying to iOS 7?

[kubamracek]

Actually, if you don't want to be blocked here, you could consider using the same trick as D29786.

[fjricci]

Turns out that's a bit tricky, because we need a thread-local AllocatorCache, which is a complex type only defined in the allocator source files.

[kubamracek]

In D29787#675861, @fjricci wrote:

Turns out that's a bit tricky, because we need a thread-local AllocatorCache, which is a complex type only defined in the allocator source files.

Move it to a header file.

[fjricci]

Uploaded a pthreads implementation which makes this patch unnecessary in D29993, D29994, D29995

[fjricci]

Reverted accidental commit. Abandoning as well, as this is no longer required.

[kubamracek]

Actually, I would still like to push towards making this change. There are other issue with supporting ios/iossim 7.0.

[kubamracek]

I'll commandeer this, hope you don't mind.

[kubamracek]

@kcc, do you still need ios 7.0 support?

[kcc]

In D29787#680579, @kubamracek wrote:

@kcc, do you still need ios 7.0 support?

Nope.

[fjricci]

Given @kcc's comment, LGTM.

cmake/config-ix.cmake

else()
       message(ERROR "Could not detect OS X Sysroot. Either install Xcode or the Apple Command Line Tools")
     endif()
   endif()
 
   if(COMPILER_RT_ENABLE_IOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)
     set(DARWIN_ios_MIN_VER_FLAG -miphoneos-version-min)
     set(DARWIN_ios_SANITIZER_MIN_VER_FLAG
-      ${DARWIN_ios_MIN_VER_FLAG}=7.0)
+      ${DARWIN_ios_MIN_VER_FLAG}=8.0)
   endif()
   if(COMPILER_RT_ENABLE_WATCHOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS watchos)
     set(DARWIN_watchos_MIN_VER_FLAG -mwatchos-version-min)
     set(DARWIN_watchos_SANITIZER_MIN_VER_FLAG
       ${DARWIN_watchos_MIN_VER_FLAG}=2.0)
   endif()
   if(COMPILER_RT_ENABLE_TVOS)