The IAR makefiles should use the -L option to set the linker library search path, then list library names with paths rooted in that search path.  Concretely, we should do this:

• -L $(SDK_INSTALL_DIR)/source
• ti/drivers/lib/drivers_msp432e4.arm4f
• ti/dpl/lib/dpl_msp432e4.arm4f

rather than this:

• $(SDK_INSTALL_DIR)/source/ti/drivers/lib/drivers_msp432e4.arm4f
• $(SDK_INSTALL_DIR)/source/ti/dpl/lib/dpl_msp432e4.arm4f

This change would make them consistent with the approach used by other toolchains, and would better position us for the move to GenLibs (which also requires users set the linker library search path).