This patch solves some issues when Linuxbrew runs on FreeBSD, but it can't detect system gcc or clang. So you can't install packages...

linuxbrew-on-freebsd.diff

diff --git a/Library/Homebrew/cmd/install.rb b/Library/Homebrew/cmd/install.rb
index 0a7a8dc8b..7bea96cf8 100644
--- a/Library/Homebrew/cmd/install.rb
+++ b/Library/Homebrew/cmd/install.rb
@@ -286,7 +286,7 @@ module Homebrew
   def symlink_ld_so
     ld_so = HOMEBREW_PREFIX/"lib/ld.so"
     return if ld_so.readable?
-    sys_interpreter = ["/lib64/ld-linux-x86-64.so.2", "/lib/ld-linux.so.3", "/lib/ld-linux.so.2", "/lib/ld-linux-armhf.so.3"].find do |s|
+    sys_interpreter = ["/compat/linux/lib64/ld-linux-x86-64.so.2", "/compat/linux/lib/ld-linux.so.3", "/compat/linux/lib/ld-linux.so.2", "/compat/linux/lib/ld-linux-armhf.so.3"].find do |s|
       Pathname.new(s).executable?
     end
     raise "Unable to locate the system's ld.so" unless sys_interpreter
diff --git a/Library/Homebrew/cmd/update.sh b/Library/Homebrew/cmd/update.sh
index b4904e4b8..04e553ef1 100644
--- a/Library/Homebrew/cmd/update.sh
+++ b/Library/Homebrew/cmd/update.sh
@@ -559,7 +559,7 @@ EOS
       export HOMEBREW_UPDATE_BEFORE"$TAP_VAR"="$CURRENT_REVISION"
       export HOMEBREW_UPDATE_AFTER"$TAP_VAR"="$CURRENT_REVISION"
     else
-      merge_or_rebase "$DIR" "$TAP_VAR" "$UPSTREAM_BRANCH"
+      # merge_or_rebase "$DIR" "$TAP_VAR" "$UPSTREAM_BRANCH"
       [[ -n "$HOMEBREW_VERBOSE" ]] && echo
     fi
   done
diff --git a/Library/Homebrew/extend/os/development_tools.rb b/Library/Homebrew/extend/os/development_tools.rb
index 5bd5cb81a..11809e651 100644
--- a/Library/Homebrew/extend/os/development_tools.rb
+++ b/Library/Homebrew/extend/os/development_tools.rb
@@ -1,2 +1 @@
 require "development_tools"
-require "extend/os/mac/development_tools" if OS.mac?
diff --git a/Library/Homebrew/extend/os/emoji.rb b/Library/Homebrew/extend/os/emoji.rb
index 8fd99e1d3..3d7db9586 100644
--- a/Library/Homebrew/extend/os/emoji.rb
+++ b/Library/Homebrew/extend/os/emoji.rb
@@ -1,3 +1,2 @@
 require "os"
 require "emoji"
-require "extend/os/mac/emoji" if OS.mac?
diff --git a/Library/Homebrew/extend/os/hardware.rb b/Library/Homebrew/extend/os/hardware.rb
index 6128072f4..2404197c0 100644
--- a/Library/Homebrew/extend/os/hardware.rb
+++ b/Library/Homebrew/extend/os/hardware.rb
@@ -1,5 +1 @@
-if OS.mac?
-  require "extend/os/mac/hardware/cpu"
-elsif OS.linux?
-  require "extend/os/linux/hardware/cpu"
-end
+require "extend/os/linux/hardware/cpu"
diff --git a/Library/Homebrew/os.rb b/Library/Homebrew/os.rb
index 66e579844..da44e68c3 100644
--- a/Library/Homebrew/os.rb
+++ b/Library/Homebrew/os.rb
@@ -1,12 +1,10 @@
 module OS
   def self.mac?
-    return false if ENV["HOMEBREW_TEST_GENERIC_OS"]
-    RUBY_PLATFORM.to_s.downcase.include? "darwin"
+    return false
   end
 
   def self.linux?
-    return false if ENV["HOMEBREW_TEST_GENERIC_OS"]
-    RUBY_PLATFORM.to_s.downcase.include?("linux") || RbConfig::CONFIG["host_os"].downcase.include?("linux")
+    return true
   end
 
   ::OS_VERSION = ENV["HOMEBREW_OS_VERSION"]
diff --git a/Library/Homebrew/os/mac/pathname.rb b/Library/Homebrew/os/mac/pathname.rb
index 28907cdf4..6c599745c 100644
--- a/Library/Homebrew/os/mac/pathname.rb
+++ b/Library/Homebrew/os/mac/pathname.rb
@@ -1,9 +1,4 @@
 class Pathname
-  if OS.mac?
-    require "os/mac/mach"
-    include MachOShim
-  elsif OS.linux?
     require "os/linux/elf"
     include ELF
-  end
 end
diff --git a/Library/Homebrew/requirements/glibc_requirement.rb b/Library/Homebrew/requirements/glibc_requirement.rb
index fdbd2cd0a..2677fe7d5 100644
--- a/Library/Homebrew/requirements/glibc_requirement.rb
+++ b/Library/Homebrew/requirements/glibc_requirement.rb
@@ -13,7 +13,7 @@ class GlibcRequirement < Requirement
 
   def self.system_version
     return @system_version if @system_version
-    libc = ["/lib/x86_64-linux-gnu/libc.so.6", "/lib64/libc.so.6", "/lib/libc.so.6", "/lib/i386-linux-gnu/libc.so.6", "/lib/arm-linux-gnueabihf/libc.so.6"].find do |s|
+    libc = ["/compat/linux/lib/x86_64-linux-gnu/libc.so.6", "/compat/linux/lib64/libc.so.6", "/compat/linux/lib/libc.so.6", "/compat/linux/lib/i386-linux-gnu/libc.so.6", "/compat/linux/lib/arm-linux-gnueabihf/libc.so.6"].find do |s|
       Pathname.new(s).executable?
     end
     raise "Unable to locate the system's glibc" unless libc
diff --git a/Library/Homebrew/utils/git.rb b/Library/Homebrew/utils/git.rb
index 1b4d24894..21d011fc7 100644
--- a/Library/Homebrew/utils/git.rb
+++ b/Library/Homebrew/utils/git.rb
@@ -1,20 +1,20 @@
 module Utils
   def self.git_available?
     return @git if instance_variable_defined?(:@git)
-    @git = quiet_system HOMEBREW_SHIMS_PATH/"scm/git", "--version"
+    @git = quiet_system "/usr/local/bin/git", "--version"
   end
 
   def self.git_path
     return unless git_available?
     @git_path ||= Utils.popen_read(
-      HOMEBREW_SHIMS_PATH/"scm/git", "--homebrew=print-path"
+      "/usr/local/bin/git", "--homebrew=print-path"
     ).chuzzle
   end
 
   def self.git_version
     return unless git_available?
     @git_version ||= Utils.popen_read(
-      HOMEBREW_SHIMS_PATH/"scm/git", "--version"
+      "/usr/local/bin/git", "--version"
     ).chomp[/git version (\d+(?:\.\d+)*)/, 1]
   end
 

I modified your patch and now it works almost fully. Thank you!
http://qiita.com/cielavenir/items/741921fcecb281555f77

@cielavenir （*´・ω・） nice work