Added documentation for minGW cross-compiling.

Former-commit-id: db4a2047b15d423ac44fa1758f9e5c6e86c6ec06

README.minGW

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+== Info for Building TAU with the minGW cross-compilers for use on
+32-bit Windows ==
+
+Requirements:
+
+* i586-mingw32msvc-gcc
+* i586-mingw32msvc-g++
+* i586-mingw32msvc-ar
+
+in your path.
+
+Limitations:
+
+* Only static libraries
+* No symbol demangling
+* No signal processing
+
+Instructions:
+
+%> ./configure -DISABLESHARED
+%> patch include/Makefile minGW.patch
+
+Libraries will be placed in 'mingw32/lib'.

minGW.patch

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+31,34c31,34
+< CONFIG_ARCH=x86_64
+< TAU_ARCH=x86_64
+< CONFIG_CC=gcc
+< CONFIG_CXX=g++
+---
+> CONFIG_ARCH=mingw32
+> TAU_ARCH=mingw32
+> CONFIG_CC=i586-mingw32msvc-gcc
+> CONFIG_CXX=i586-mingw32msvc-g++
+55c55
+< USER_OPT=-g -O2
+---
+> USER_OPT=-g -O2 -DTAU_WINDOWS -DTAU_DISABLE_SIGUSR -DTAU_MINGW -DTAU_ENABLE
+342c342
+< PLATFORM_O       = TauLinuxTimers.o       #ENDIF##LINUXTIMERS#
+---
+> # PLATFORM_O       = TauLinuxTimers.o       #ENDIF##LINUXTIMERS#
+383c383
+< PROFILEOPT31       = -DTAU_LINUX_TIMERS    #ENDIF##LINUXTIMERS#
+---
+> #PROFILEOPT31       = -DTAU_LINUX_TIMERS    #ENDIF##LINUXTIMERS#
+418c418
+< PROFILEOPT60           = -DTAU_LARGEFILE -D_LARGEFILE64_SOURCE     #ENDIF##TAU_LARGEFILE#
+---
+> #TAU_LARGEFILE##TAU_LARGEFILE#PROFILEOPT60           = -DTAU_LARGEFILE -D_LARGEFILE64_SOURCE     #ENDIF#
+436c436
+< PROFILEOPT75 = -DTAU_BFD #ENDIF##TAU_BFD#
+---
+> #PROFILEOPT75 = -DTAU_BFD #ENDIF##TAU_BFD#
+439c439
+< PROFILEOPT77 = -DHAVE_GNU_DEMANGLE #ENDIF##TAU_DEMANGLE#
+---
+> #PROFILEOPT77 = -DHAVE_GNU_DEMANGLE #ENDIF##TAU_DEMANGLE#
+778c778
+< TAU_AR                 = ar             #ENDIF#
+---
+> TAU_AR                 = i586-mingw32msvc-ar #ENDIF#
+813c813
+< BFDLIBS=-lbfd
+---
+> #BFDLIBS=-lbfd