libc++ build step

[frankomosh]

A fix may be needed in MemorySanitizerLibcxxHowTo.md and MemorySanitizerBootstrappingClang.md.

I came across these and think the wiki should reflect some changes described here:

Change:

MemorySanitizerLibcxxHowTo.md:

• Line 56: cmake -GNinja ../llvm → cmake -GNinja ../runtimes
• Line 58: LLVM_ENABLE_PROJECTS="libcxx;libcxxabi" → LLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"
• Line 73: dead svn co -r613 http://googletest.googlecode.com/svn/trunk → git clone --depth=1 https://github.com/google/googletest.git
• Line 77: make -j12 → make -j$(nproc)

MemorySanitizerBootstrappingClang.md:

• Line 29: cmake -GNinja ../llvm → cmake -GNinja ../runtimes
• Line 31: LLVM_ENABLE_PROJECTS="libcxx;libcxxabi" → LLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"

Note: the LLVM_ENABLE_PROJECTS="clang;lld" line in MemorySanitizerBootstrappingClang.md is left untouched — clang and lld are genuine LLVM projects, not runtimes, so that line is correct.

Happy to provide the raw diff if anyone finds it useful.

Diff for MemorySanitizerLibcxxHowTo.md:

-cmake -GNinja ../llvm \
+cmake -GNinja ../runtimes \
 	-DCMAKE_BUILD_TYPE=Release \
-	-DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" \
+	-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \

-$ svn co -r613 http://googletest.googlecode.com/svn/trunk googletest
+$ git clone --depth=1 https://github.com/google/googletest.git

-$ make -j12
+$ make -j$(nproc)

Diff for MemorySanitizerBootstrappingClang.md:

-cmake -GNinja ../llvm \
+cmake -GNinja ../runtimes \
 	-DCMAKE_BUILD_TYPE=Release \
-	-DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" \
+	-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \