Merge pull request JuliaLang#12101 from odysseus9672/patch-1

External Conflict Troubleshooting

Author: tkelman

README.md

@@ -217,13 +217,15 @@ Illegal Instruction error | Check if your CPU supports AVX while your OS does no
 
 ### OS X
 
-It is essential to use a 64-bit gfortran to compile Julia dependencies. The gfortran-4.7 (and newer) compilers in brew and MacPorts work for building Julia.
+It is essential to use a 64-bit gfortran to compile Julia dependencies. The gfortran-4.7 (and newer) compilers in Brew, Fink, and MacPorts work for building Julia.
 Clang is now used by default to build Julia on OS X (10.7 and above). It is recommended that you upgrade to the latest version of Xcode (at least 4.3.3.). You need to have the Xcode command line utilities installed (and updated): run `xcode-select --install` in the terminal (in Xcode prior to v5.0, you can alternatively go to Preferences -> Downloads and select the Command Line Utilities). This will ensure that clang v3.1 is installed, which is the minimum version of `clang` required to build Julia. On OS X 10.6, the Julia build will automatically use `gcc`.
 
 If you have set `LD_LIBRARY_PATH` or `DYLD_LIBRARY_PATH` in your `.bashrc` or equivalent, Julia may be unable to find various libraries that come bundled with it. These environment variables need to be unset for Julia to work.
 
 If you see build failures in OpenBLAS or if you prefer to experiment, you can use the Apple provided BLAS in vecLib by building with `USE_SYSTEM_BLAS=1`. Julia does not use the Apple provided LAPACK, as it is too old.
 
+When building Julia, or its dependencies, libraries installed by third party package managers can redirect the compiler to use an incompatible version of the software it is looking for. One example of this happening is when a piece of software called the "linker" gives an error involving "Undefined symbols." If that happens, you can usually figure out what software package is causing the error from the names in the error text. This sort of error can be bypassed by, temporarily, uninstalling the offending package. If the offending package cannot be uninstalled by itself, it may be possible to just uninstall the development headers (for example: a package ending in "-dev" in Fink).
+
 ### FreeBSD
 
 On *FreeBSD Release 9.0*, install the `gcc47`, `git`, and `gmake` packages/ports, and compile Julia with the command: